Chapter 12 SG Review

8th- Advanced

• 1. Define Work– When you exert force on an object and it causes an

object to move some distance.• 2. When is work done.– When an object moves a distance.

• 3. To do work what direction does the motion have to be?– Parallel to the direction of the force applied.

• 4. What is the equation for work?– Work = force x Distance

• 5. What is the unit for work?– Joules

• 6. Define power?– Amount of work done in a unit of time.

• 7. What is the equation for power?– Power = work/time

• 8. What is the unit for power?– Watts

• 9. What is a machine?– A device that makes work easier.

• 10. What are 3 ways in which a machine makes work easier?– 1) changes the amt of force you exert 2) changes the

distance over which you exert a force 3) changes the direction in which you exert the force

• 11. What is input force?– The force you exert on the machine.

• 12. what is an output force?– The force the machine exerts on an object

• 13. What is input work?– Input force X input distance

• 14. What is output work?– Output force X output distance

• 15. If the amount of work stays the same a decrease in force means a(n) ________ in distance.– Increase

• 16. What happens if output force is less than input force?– Mechanical advantage would be less than 1

• 17. What is mechanical advantage?– The number of times a machine increases a force

exerted on it. • 18. How do you calculate mechanical advantage?– Output force/ input force

• 19. What force always causes some work to be wasted?– Friction

• 20. What is efficiency?– Expressed as a percent and compares the output

work to the input work.• 21. Why is output always less than input in real

situations?– In every machine, some work is wasted overcoming

the force of friction. • 22. How do you calculate efficiency?– Efficiency = output work/ input work x 100%

• 23. What is a machines ideal mechanical advantage?– Output force/ input force (IDEAL= NO FRICTION)

• 24. What does 1 horsepower equal?– 745 watts

• 25. What are the 6 basic types of machines?– 1) wheel and axle 2) inclined plane 3) screw– 4) lever 5) pulley 6) wedge

• 26. As the length of the incline plane increases what happens to your input force?– It decreases

• 27. What are 5 examples of wedges?– 1) front two teeth 2) door stopper 3) wedge heel of

your shoe 4) scissors 5) end of an ax

• 28. What is a screw?– An inclined plane wrapped around a cylinder

• 29. What is a lever?– A rigid bar that is free to pivot, or rotate, on a fixed

point• 30. What is a fulcrum?– The fixed point that a lever pivots around.

• 31. How many different types of levers are there? How are they classified?– 3 Different types of levers– Levers are classified according to the location of the

fulcrum relative to the input and output forces.

• 32. How do you determine the mechanical advantage of a pulley system?– The ideal mechanical advantage of a pulley is equal to

the number of sections of rope that support the object. • 33. Joe applies 250N force to move a bolder 40m,

how much work did Joe do?– W = F x D– W= 250 x 40 = 10,000J

• 34. How far will 100 J raise a 2Kg mass?– W = F x D– 100 J = 2(9.8 m/s2) x D– 5.1 Meters

• 35. How much power does it take to do 104J of work in 8 seconds?– P = work/ time– P= 104J/ 8 Seconds– P= 13 Watts

• 36. How much power does it take to lift 50 N 20 m in 10 seconds– P = (F x D)/ time– P= (50N x 20m) / 10seconds– P = 100 Watts

• 37. If a motor uses 1500J of energy to raise 10Kg 10m high, what is the efficiency of the motor– F = ma– F= 10kg (9.8)= 98 N– W= F x D– W= 98N x 10M= 980J– Efficiency = (output work/ input work) x 100%– E = (980/ 1500) x 100 = 65%

• 38. A 300 watt electrical motor takes 10 seconds to raise 5 kg 40 m. What is the efficiency of the motor.– F = ma– F= 5kg x 9.8 = 49N– W= F x D– W = 49n x 40m= 1960J– P= W/Time– P= 1960J / 10sec = 196 Watts– Efficiency = output/input x 100– Efficiency = (196/300) x 100 = 65%

• 39. What is the efficiency of a block and tackle if a 60 kg mass pulls 30m of rope to a raise 500kg piano 2m.– Efficiency = output work / input work x 100– First you can to calculate the work– Before you can do that you have to calculate the

force of each.– F = ma, w = F x D – E = (500kg (9.8) x 2m)/ (60kg (9.8) x 30m) x 100%– E = 55%