review homework. p2 – forces and motion lesson 2: d-t and v-t graphs

Review Homework

Keywords: Distance-Time, Velocity-Time, Gradient, Keywords: Distance-Time, Velocity-Time, Gradient,

1. A ferrari was travelling at 20 m/s behind a lorry. It pulled out to overtake and accelerated at 4 m/s2 for 2 seconds. What was its new speed ?

TimeonAcceleratispeedinChange ssm 2/4 2 sm /8

New Speed = Old Speed + Change in Speed

= 20 m/s + 8 m/s

= 28 m/s

v

ta

You can draw a graph to show how an object travels.

Lets plot one together


Distance-Time Graphs

A family travel by car from London to Manchester and their journey is shown below. The family stop in Birmingham for lunch for 1 hour and in Lymm to collect friends for 1 hour.

Journey Distance (miles) Time (hours)

London to Birmingham

120 2:30

Birmingham to Lymm 75 1:30

Lymm to Manchester 15 0:30


Journey Distance (miles)

Time (hour

s)

London to Birmingham

120(120)

2:30(2:30)

Break 0(120)

1:00(3.30)

Birmingham to Lymm

75(195)

1:30(5:00)

Break 0(195)

1:00(6:00)

Lymm to Manchester

15(210)

0:30(6:30)

Time (hours)

Dis

pla

em

ent

(mile

s)

Displacement time graph to show a journey from London to

Manchester

0 1 2 3 4 5 6 7

075

150

225

x x

x xx


Time (hours)

Dis

pla

cem

ent

(mile

s)Displacment time graph to show a

journey from London to Manchester

0 1 2 3 4 5 6 7

075

150

225

x x

x xx

Stationary for lunch in Birmingham

Stationary in Lymm Arrive in

Manchester

Leave London – then travel at constant speed


Important things to know:

• The gradient = speed• Flat section are where it’s stopped• The steeper the slope, the faster it is going• Downhill sections means that it’s going towards its starting point. • Curves represent acceleration• A steepening curve means it’s speeding up • A leaving off curve means it’s slowing down


Calculating Speed

You can use a distance-time graph to calculate the speed. All you need to do is work out the gradient.

Gradient = Vertical Horizontal


Time (hours)

Dis

tance

(m

iles)

0 1 2 3 4 5

075

150

x

e.g. 150

5 = 30 mph

(Remember to use the units on the axis)

Are you now able to….

I still feel unsure. I need some more help to understand.

I feel ok. I need to do some more work to check my understanding.

I am happy and feel I understand and can explain the main points.


Another graph that can be plotted is a velocity-time graph.

Lets plot one together


Velocity-Time Graphs

1.A car accelerates to 30mph in 20s.2.Car travels at 30mph for 40s3.The car then decelerates to 10mph in 20s4.The car then travels at 10mph for 30s. 5.The car then comes to a stop in 10s.

Draw a V-T of the journey.


Velocity-Time Graphs – Questions….

1.What is the cars acceleration in the first 20s?2.How far did the car travel when it travelled at a constant speed of 30m/s?


Time (s)

Avera

ge S

peed (

mph)

Velocity-Time graph

0 30 60 90 110 140

010

20

30

x



1.A car accelerates to 30mph in 20s.2.Car travels at 30mph for 40s (60s)3.The car then decelerates to 10mph in 20s (80s)4.The car then travels at 10mph for 30s (110s). 5.The car then comes to a stop in 10s (120s).

Draw a V-T of the journey.

x

x x

xx

Time (s)

Avera

ge S

peed (

mph)

Velocity-Time graph

0 30 60 90 110 140

010

20

30

x


Acceleration at from 0 to 30?

x

x x

xx

a = change in v time taken

Therefore acceleration is the gradient:

30 = 1.5 m/s2 20

Time (s)

Avera

ge S

peed (

mph)

Velocity-Time graph

0 30 60 90 110 140

010

20

30

x



How far has he travelled when at a constant speed of 30mph?

Area = distance travelled. x

x x

xx

Area = length x widthArea = length x width

30mph x 40s = Area30mph x 40s = Area

120 miles120 miles

Important things to know:

• The gradient = acceleration • Flat section are travelling at a steady speed• The steeper the slope, the greater the acceleration. • Uphill sections are acceleration. • Downhill section are deceleration• The area under any section is the distance travelled in that time interval. • A curve means a changing acceleration.


Velocity/TimeDistance/Time

Stopped

Const’ Velocity

Const’ Accel’n

D

t

D

t

D

t

V

t

V

t

V

t

Gradient = Velocity

Gradient = Accel’nArea = Distance travelled

Are you now able to….

I still feel unsure. I need some more help to understand.

I feel ok. I need to do some more work to check my understanding.

I am happy and feel I understand and can explain the main points.


review homework. p2 – forces and motion lesson 2: d-t and v-t graphs

Documents

velocitytime graphsa

velocitytime graphs

time hoursdistance miles0

car travels

sthe car

new speed

constant speed

old speed change