ms.raja elgady/energy power and work elgady/energy power and work 1- (a) state the energy changes...

MS.RAJA ELGADY/ENERGY POWER AND WORK1- (a) State the energy changes that take place when

(i) a cyclist rides down a hill without pedalling,

............................................................................................................................. .....

..................................................................................................................................

(ii) a cyclist pedals up a hill at a constant speed.

............................................................................. .....................................................

............................................................................................................................. ..... [3]

(b) A car of mass 940kg is travelling at 16m/s.

(i) Calculate the kinetic energy of the car.

kinetic energy = .................................................. [2]

(ii) The car is brought to rest by applying the brakes.

The total mass of the brakes is 4.5kg. The average specific heat capacity of the brakematerial is 520J / (kg °C).

Calculate the rise in temperature of the brakes. Assume there is no loss of thermalenergy from the brakes.

rise in temperature = .................................................. [3] [Total: 8]

MS.RAJA ELGADY/ENERGY POWER AND WORK2- Fig. 3.1 shows an early water-powered device used to raise a heavy load. The heavy load rests on

piston B.cylinder A

water

piston A

cylinder B

load

piston B

connecting rod connecting rod

pivot beam

Fig. 3.1 (not to scale)

Initially, a large weight of water in cylinder A pushes piston A down. This causes the left-hand endof the beam to move down and the right-hand end of the beam to move up. Piston B rises, liftingthe heavy load.

(a) The weight of water in cylinder A is 80kN.

Calculate the mass of water in cylinder A.

mass = ................................................ [2]

77MS.RAJA ELGADY/ENERGY POWER AND WORK(b) The density of water is 1000kg /m3.

Calculate the volume of water in cylinder A.

volume = ................................................ [2]

(c) Piston A moves down a distance of 4.0m.

Calculate the gravitational potential energy lost by the water.

loss of gravitational potential energy = ................................................ [2]

(d) The heavy load lifted by piston B gains 96kJ of gravitational potential energy.

Calculate the efficiency of the device.

efficiency = ................................................ [2]

[Total: 8]

88MS.RAJA ELGADY/ENERGY POWER AND WORK3- A diver climbs some steps on to a fixed platform above the surface of the water in a swimming-pool.

He dives into the pool. Fig. 2.1 shows the diver about to enter the water.

8.0 m

Fig. 2.1

The mass of the diver is 65kg. The platform is 8.0m above the surface of the water.

(a) Calculate

(i) the increase in the gravitational potential energy of the diver when he climbs up to theplatform.

increase in gravitational potential energy = ................................................[1]

(ii) the speed with which the diver hits the surface of the water. Ignore any effects of airresistance.

speed = ................................................[4]

99MS.RAJA ELGADY/ENERGY POWER AND WORK(b) In another dive from the same platform, the diver performs a somersault during the descent.

He straightens, and again enters the water as shown in Fig. 2.1.

Discuss whether the speed of entry into the water is greater than, less than or equal to thespeed calculated in (a)(ii). Ignore any effects of air resistance.

............................................................................................................................. ......................

...................................................................................................................................................

............................................................................................................................. ......................

......................................................................................................................................... ......[3]

[Total: 8]

1010

MS.RAJA ELGADY/ENERGY POWER AND WORK4- Fig. 3.1 shows a skier taking part in a downhill race.

Fig.

3.1

(a) The mass of the skier, including his equipment, is 75kg. Inthe ski race, the total vertical change in height is 880m.

Calculate the decrease in the gravitational potential energy(g.p.e.) of the skier.

decrease in g.p.e. = ...........................................................[2]

(b) The skier starts from rest. The total distance travelled by theskier during the descent is

2800m. The average

resistive force on the

skier is 220N. Calculate

(i) the work done against the resistive force,

work done = ...........................................................[2]

(ii) the kinetic energy of the skier as he crosses the finishingline at the end of the race.

1111

MS.RAJA ELGADY/ENERGY POWER AND WORKkinetic energy = ...........................................................[2]

(c) Suggest why the skier bends his body as shown in Fig. 3.1.

...................................................................................................................

............................[1] [Total: 7]

1212

MS.RAJA ELGADY/ENERGY POWER AND WORK5- Fig. 3.1 shows the descent of a sky-diver from a stationaryballoon.

ForExaminer’s

Use

2000 m

sky-diver

parachute

500m

Fig. 3.1 (not to scale)

The sky-diver steps from the balloon at a height of 2000m and accelerates downwards.

His speed is 52m/s at a height of 500m.

He then opens his parachute. From 400m to ground level, he falls at constant speed.

(a) The total mass of the sky-diver and his equipment is 92kg.

(i) Calculate, for the sky-diver,

1. the loss of gravitational potential energy in the fall from 2000m to 500m,

loss of gravitational potential energy = .................................................. [2]

2. the kinetic energy at the height of 500m.

1313

MS.RAJA ELGADY/ENERGY POWER AND WORKkinetic energy = .................................................. [2]

1414

MS.RAJA ELGADY/ENERGY POWER AND WORK6- (a) Fig. 4.1 shows some gas contained in a cylinder by a heavy piston. The piston can move

up and down in the cylinder with negligible friction.For

Examiner’sUse

heavypiston

atmosphere cylinder

gas

Fig. 4.1

There is a small increase in the pressure of the atmosphere above the piston.

(i) On Fig. 4.1, draw a possible new position for the lower face of the piston. [1]

(ii) Explain, in terms of the molecules of the gas and the molecules of the atmosphere,your answer to (a)(i).

..................................................................................................................................

............................................................................................................................. .....

..................................................................................................................................

............................................................................................................................. .....

..................................................................................................................................

............................................................................................................................. [3]

1515MS.RAJA ELGADY/ENERGY POWER AND WORK

(b) The pressure of the atmosphere above the piston returns to its original value, and thepiston returns to its original position, as shown in Fig. 4.2.

ForExaminer’s

Use

heavypiston

atmosphere cylinder

gas

Fig. 4.2

The gas, piston and cylinder are now heated to a much higher temperature.

(i) On Fig. 4.2, draw a possible new position for the lower face of the piston. [1]

(ii) Explain, in terms of the molecules of the gas and the molecules of the atmosphere,your answer to (b)(i).

............................................................................................................................. .....

............................................................................................................................ ......

............................................................................................................................. .....

.................................................................................................................... ..............

............................................................................................................................. [2]

[Total: 7]

1616

MS.RAJA ELGADY/ENERGY POWER AND WORK7- A cyclist rides up and then back down the hill shown in Fig.3.1.

top of hill

ForExaminer’s

Use

14 m

starting andfinishing point

Fig. 3.1

The cyclist and her bicycle have a combined mass of 90 kg. She pedals up to the top andthen stops. She turns around and rides back to the bottom without pedalling or using herbrakes.

(a) Calculate the potential energy gained by the cyclist and her bicycle when she hasreached the top of the hill.

potential energy = ................................................ [2]

(b) Calculate the maximum speed she could have when she arrives back at the startingpoint.

speed = ................................................ [3]

(c) Explain why her actual speed will be less than that calculated in (b).

..........................................................................................................................................

............................................................................................................................. .............

..........................................................................................................................................

............................................................................................................................. ....... [1]

[Total: 6]


8- (a) Energy from the Sun evaporates water from the sea. Some of this water eventually drives ahydroelectric power station. Give an account of the processes and energy changes involved.

.................................................................................. .................................................................

............................................................................................................................. ......................

...................................................................................................................................................

............................................................................................................................. ......................

............................................................................................................................. ......................

.......................................................................................... .........................................................

............................................................................................................................. ......................

...................................................................................................................................................

............................................................................................................................. ......................

............................................................................................................................. ..................[4]

(b) In a hydroelectric power station, 200000kg of water per second fall through a vertical distanceof 120m. The water passes through turbines to generate electricity, and leaves the turbineswith a speed of 14m/s.

(i) Calculate the gravitational potential energy lost by the water in 1 second. Use g = 10m/s2.

potential energy lost = ............................................................[2]

(ii) Calculate the kinetic energy of the water leaving the turbines in 1 second.

kinetic energy = ............................................................[2]

[Total: 8]

1818

MS.RAJA ELGADY/ENERGY POWER AND WORK9- A wind turbine has blades, which sweep out an area of diameter 25m.

25 m

ForExaminer’s

Use

blades

Fig. 5.1

(a) The wind is blowing directly towards the wind turbine at a speed of 12m/s. At this windspeed, 7500kg of air passes every second through the circular area swept out by theblades.

(i) Calculate the kinetic energy of the air travelling at 12m/s, which passes throughthe circular area in 1 second.

kinetic energy = ................................................ [3]

(ii) The turbine converts 10% of the kinetic energy of the wind to electrical energy.

Calculate the electrical power output of the turbine. State any equation that youuse.

power = ................................................ [3]

2020

MS.RAJA ELGADY/ENERGY POWER AND WORK(b) On another day, the wind speed is half that in (a).

(i) Calculate the mass of air passing through the circular area per second on this day.

mass = ................................................ [1]

(ii) Calculate the power output of the wind turbine on the second day as a fraction ofthat on the first day.

fraction = ................................................ [3] [Total:

10]

2121

MS.RAJA ELGADY/ENERGY POWER AND WORK10- A farmer uses an electric pump to raise water from a river in order to fill the irrigation channels

that keep the soil in his fields moist.For

Examiner’sUse

field

water poursinto channel

electricpump

water rises 3mup tube

irrigationchannel


Fig. 5.1

Every minute, the pump raises 12kg of water through a vertical height of 3m.

(a) Calculate the increase in the gravitational potential energy of 12kg of water when it israised 3m.

increase in gravitational potential energy = ................................................ [3]

(b) Calculate the useful power output of the pump as it raises the water.

power = ................................................ [3] [Total: 6]

2323

MS.RAJA ELGADY/ENERGY POWER AND WORK(ii) The kinetic energy at 500m is not equal to the loss of

gravitational potential energy.Explain why there is a difference in the values.

...................................................................................

...............................................

...................................................................................

...............................................

....................................................................................

.......................................... [1]

(b) State

(i) what happens to the air resistance acting on the sky-diverduring the fall from

2000m to 500m,

....................................................................................

.......................................... [1]

(ii) the value of the air resistance during the fall from400m to ground.

air resistance = .................................................. [1]

[Total: 7]

2424

MS.RAJA ELGADY/ENERGY POWER AND WORK11- Fig. 3.1 shows water falling over a dam.

dam falling water

ForExaminer’s

Use

7.0m

Fig. 3.1

(a) The vertical height that the water falls is 7.0m.Calculate the potential energy lost by 1.0kg of water during the fall.

potential energy = ........................[2]

(b) Assuming all this potential energy loss is changed to kinetic energy of the water,calculate the speed of the water, in the vertical direction, at the end of the fall.

speed = ........................[3]

(c) The vertical speed of the water is less than that calculated in (b). Suggest one reasonfor this.

............................................................................................................................. .............

..................................................................................................................................... .[1]


12- An electric pump is used to raise water from a well, as shown in Fig. 3.1. pump

ground

well

Fig. 3.1

(a) The pump does work in raising the water. State an equation that could be used tocalculate the work done in raising the water.

............................................................................................................................. .........[2]

(b) The water is raised through a vertical distance of 8.0m. The weight of water raised in5.0s is 100N.

(i) Calculate the work done in raising the water in this time.

work done = .......................[1]

(ii) Calculate the power the pump uses to raise the water.

power = ........................[1]

(iii) The energy transferred by the pump to the water is greater than your answer to (i).Suggest what the additional energy is used for.

..............................................................................................................................[1]


13- A car travels around a circular track at constant speed.

(a) Why is it incorrect to describe the circular motion as having constant velocity?

............................................................................................................................................. [1]

(b) A force is required to maintain the circular motion.

(i) Explain why a force is required.

...........................................................................................................................................

............................................................................................................................. ..............

..................................................................................................................................... [2]

(ii) In which direction does this force act?

...................................................................................... ............................................... [1]

(iii) Suggest what provides this force.

............................................................................................................................. ........ [1]

[Total: 5]


14- A car travels around a circular track at constantspeed.

(a) Why is it incorrect to describe the circular motion as having constant velocity?

............................................................................................................... .............................. [1]

(b) A force is required to maintain the circular motion.

(i) Explain why a force is required.

........................................................................................................................ ...................

............................................................................................................................. ..............

.............................................................................................. ....................................... [2]

(ii) In which direction does this force act?

............................................................................................................................. ........ [1]

(iii) Suggest what provides this force.

............................................................................................................................. ........ [1]

[Total: 5]

2828

MS.RAJA ELGADY/ENERGY POWER AND WORK15- (a) State an example of the

conversion of chemical energy to

another form of energy. example

.....................................................

.....................................................

................. energy conversion

.....................................................

..................................................

[1]

(b) The electrical output of a solarpanel powers a pump. The

pump operates a water fountain.The output of the solar panel is

17 V and the current supplied tothe pump is

0.27A.

(i) Calculate the electricalpower generated by the solarpanel.

power = ................................................. [2]

(ii) The pump convertselectrical energy to kineticenergy of water with anefficiency of 35%.

Calculate the kinetic energyof the water delivered by thepump in 1 second.

kinetic energy =................................................. [2]

(iii) The pump propels 0.00014m3 of water per second. Thiswater rises vertically as a

jet.

The

density

of

water

is

1000

kg

/

m3

.

Calculate

1.

2929

MS.RAJA ELGADY/ENERGY POWER AND WORKthe mass of water

propelled by the pump in 1second,

mass = ................................................. [2]

2. the maximum height ofthe jet of water.

maximum

h

e

i

g

h

t

=

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

3030

MS.RAJA ELGADY/ENERGY POWER AND WORK.

.

.

.

.

.

.

.

.

.

.

.

.

[

2

]

[

T

o

t

a

l

:

9

]

3131

MS.RAJA ELGADY/ENERGY POWER AND WORK

16- Fig. 2.1 shows a track for a modelcar.

Examiner’sUse

PS

Q

0.4 m 0.4 m0.5 m


T R

Fig. 2.1

The car has no power supply, but can run down a sloping track due to its weight.

(a) The car is released at Q. It comes to rest just before it reaches S and rolls back.

(i) Describe the motion of the car after it starts rolling back and until iteventually comes to rest.

..................................................................................................................................

............................................................................................................................. .....

............................................................................................................................ [2]

(ii) Explain in terms of energy transformations why the car, starting at Q,cannot pass S.

..................................................................................................................................

............................................................................................................................. .....

............................................................................................................................ [1]

(b) A second car, of mass 0.12kg, is released from P. It continues until it runs off the track atT.

Calculate the maximum speed that the car could have at T assuming friction in thecar is negligible.

speed = ................................................ [3] [Total: 6]


17- Some builders decide to measure their personal power ratings using apparatus they already haveon site. Fig. 2.1 shows the arrangement they use.

pulley

rope

load

pulley

Fig. 2.1

(a) In the table below, list the three quantities they must measure in order to calculate one man’spower, and the instrument they would use for each measurement.

quantity to be measured instrument used for measurement

1.

2.

3.

[3]

(b) One workman is measured as having a power of 528W. His weight is 800N.

He can develop the same power climbing a ladder, whose rungs are 30cm apart.

How many rungs can he climb in 5s?


number of rungs = ...........................................................[3]

MS.RAJA ELGADY/ENERGY POWER AND WORK(c) The human body is only about 15% efficient when climbing ladders.

Calculate the actual energy used from the body of the workman in (b) when he climbs 20rungs.

energy used = ...........................................................[2]

[Total: 8]

MS.RAJA ELGADY/ENERGY POWER AND WORK18- (a) A man squeezes a pin between his thumb and finger, as shown in Fig.

6.1.

finger

pinhead

pin

thumb

Fig. 6.1

The finger exerts a force of 84N on the pinhead.

The pinhead has an area of 6.0 × 10–5 m2.

(i) Calculate the pressure exerted by the finger on the pinhead.

pressure = ................................................ [2]

(ii) State the value of the force exerted by the pin on the thumb.

................................................. [1]

(iii) Explain why the pin causes more pain in the man’s thumb than in his finger.

..................................................................................................................................

............................................................................................................................ [2]

ForExaminer’s

Use

MS.RAJA ELGADY/ENERGY POWER AND WORK(b) The density of the water in a swimming pool is 1000kg /m3. The pool is 3m deep.

(i) Calculate the pressure of the water at the bottom of the pool.

pressure = ................................................ [2]

(ii) Another pool has the same depth of water, but has twice the area.

State the pressure of the water at the bottom of this pool.

pressure = ................................................ [1] [Total: 8]

MS.RAJA ELGADY/ENERGY POWER AND WORK19-

(a) Name the process by which energy is released in the core of the Sun.

............................................................................................................................. ....... [1]

(b) Describe how energy from the Sun becomes stored energy in water behind a dam.

...................................................................................................................................... ....

.......................................................................................................................... ................

............................................................................................................................. .............

............................................................................................ ..............................................

............................................................................................................................. .............

.................................................................................................................................... [3]

(c) Data for two small power stations is given in Table 2.1.

ForExaminer’s

Use

input to power station output of power station

gas-fired 100MW 25MW

hydroelectric 90MW 30MW

Table 2.1

(i) State what is meant by the efficiency of a power station.

..................................................................................................................... .............

............................................................................................................................. .....

............................................................................................................. .....................

............................................................................................................................ [1]

(ii) Use the data in Table 2.1 to explain that the hydroelectric station is more efficientthan the gas-fired power station.

............................................................................................................................. .....

.................................................................................................... ..............................

............................................................................................................................. .....

............................................................................................ ......................................

............................................................................................................................ [1]

[Total: 6]

MS.RAJA ELGADY/ENERGY POWER AND WORK20- A student wishes to work out how much power she uses to lift her body when climbing a

flight of stairs.

Her body mass is 60kg and the vertical height of the stairs is 3.0m. She takes 12s to walkup the stairs.

(a) Calculate

(i) the work done in raising her body mass as she climbs the stairs,

work = ................................................ [2]

(ii) the output power she develops when raising her body mass.

power = ................................................ [2]

(b) At the top of the stairs she has gravitational potential energy.

Describe the energy transformations taking place as she walks back down the stairsand stops at the bottom.

............................................................................................................................. .............

..........................................................................................................................................

............................................................................................................................. .............

............................................................................................................................. ....... [2]

[Total: 6]

MS.RAJA ELGADY/ENERGY POWER AND WORK21- (a) On a day with no wind, a fountain in Switzerland propels 30 000kg of water per minute to a

height of 140m.

Calculate the power used in raising the water.

power = ............................................... [4]

(b) The efficiency of the pump which operates the fountain is 70%.

Calculate the power supplied to the pump.

power = ............................................... [3]

(c) On another day, a horizontal wind is blowing. The water does not rise vertically.

Explain why the water still rises to a height of 140m.

...................................................................................................................................................

............................................................................................................................. ................. [1]

[Total: 8]

ms.raja elgady/energy power and work elgady/energy power and work 1- (a) state the energy changes...

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