1. How much work is done in lifting a 300 Newton rock 10 meters off the ground?
2. A force of 200 Newtons is needed in order to push a wheelbarrow that weighs 1000 Newtons. If the wheelbarrow is pushed 30 meters, how much work is done on the wheelbarrow?
3. A force sets an object in motion. When the force is multiplied by the time of its application, we call the quantity impulse, which changes the momentum of that object. What do we call the quantity force x distance, and what quantity can this change?
4. Work is required to lift a barbell. How many times more work is required to lift the barbell three times high?
5. Which requires more work, lifting a 10 kg load a vertical distance of 2 m or lifting a 5 kg load a vertical distance of 4 m?
6. How many joules of work are done on an object when a force of 10 N pushes it a distance of 10 m?
7. Calculate the work done when a 20 N force pushes a cart 3.5 m.
8. Calculate the work done in lifting a 500.0 N barbell 2.2m above the floor. What is the potential energy of the barbell when it is lifted to this height?
9. (a) Calculate the work needed to lift a 90.0 N block of ice a vertical distance of 3.0 m. What PE does it have? (b) When the same block of ice is raised the same vertical distance by pushing it up a 5.0 m long ramp, only 54.0 N of pushing force are required. Calculate the work done to push the block up the plane. What PE does it have? (c) Is this ramp ideal or not? Explain how you know.
10. (a) Calculate the kinetic energy of a 3.1 kg toy cart that moves at 4.8 m/s. (b) Calculate the kinetic energy of the same cart at twice the speed.
11. Suppose an automobile has 20,000 J of kinetic energy. When it moves at twice the speed, what will be its kinetic energy? What's its kinetic energy at three times the speed?
12. If a mouse and an elephant both run with the same kinetic energy, can you say which is running faster? Explain in terms of the equation for KE.
13. A hammer falls off a rooftop and strikes the ground with a certain KE. If it fell from a roof that was four times higher, how would its KE of impact compare? Its speed of impact? (Neglect air resistance.)
14. (a) If you do 100 J of work to elevate a bucket of water, what is its gravitational potential energy relative to the starting position? (b) What would the gravitational potential energy be if the bucket were raised twice as high? (c) How much work would the bucket do on its surroundings as it fell back to its starting position?
15. An astronaut in full space gear climbs a vertical ladder on the earth. Later, the astronaut makes the same climb on the moon. In which locations does the gravitational potential energy of the astronaut change more? Explain.
16. Calculate the change in potential energy of 8.00 x 106 kg of water dropping 50.0 m over Niagara Falls.
17. If 8.00 x 106 kg of water flows over Niagara Falls each second, calculate the power available at the bottom of the falls.
18. A force of 110 Newtons is required to move an object down the hall a distance of 20.0 meters in 8.0 s. What power was required to do this?
19. A power shovel raised 5000 Newtons of dirt to a height of 10 meters
in 5 seconds. Compute the
20. Sam pushes his car 5.00 meters to the side of the road in 15.0 seconds. The car weighs 5000 Newtons and Sam pushes with 754 Newtons. How much power is required?
21. What is the power of a machine that can do 50,000 joules of work in 50 seconds'?
22. If you lifted a 600 N box to a height of 3 meters, in 10 seconds. How much power did you expend?
23. How much power is required to do 100.0 J of work on an object in a time of 0.50 s? How much power is required if the same work is done in 1.0s?
24. A certain car can go from 0 to 100 km/h in 10 s. If the engine delivered twice the power to the wheels, how many seconds would it take?
25. Calculate the power expended when a 500.0 N barbell is lifted 2.2m in 2.0 s.
26. Peter used a stick 1.8 meters long to push aside a large rock in the yard. The fulcrum was 0.3 meters from the resistance. What is the ideal mechanical advantage of the stick?
27. Ann and her mother returned home to find that a large box had been delivered and left on their doorstep. The mailing label indicated that the weight of the box and its contents was 500 Newtons. Ann's mother went to the garage and returned with a cart and crowbar. The crowbar had a mechanical advantage of 10. Calculate the effort force needed to lift the box with the crowbar so the cart could be slid underneath the box.
28. Karen was helping her father repair the roof of their house. They needed to bring a variety of tools and materials up to the roof. Karen suggested constructing a pulley. The heaviest load weighed about 400 N. Karen wanted to exert a minimum force of 100 Newtons. How many strings should Karen's pulley have?
29. Carol wanted to put a 250 Newton box up on a shelf that was 0.75 meters above the floor. She set up a board 2.00 meters long to use as an inclined plane. Neglecting friction, calculate the amount of force Carol needed to exert while sliding the box up to the shelf using the inclined plane.
30. How efficient is a pulley system if it enables you to lift a 700.0 Newton engine 0.550 meters if you exerted 35.7 Newtons of force while pulling 11.43 meters of rope?
31. A car jack has an effort arm of 45 centimeters and a resistance arm of 7.3 cm. What is the ideal mechanical advantage?
32. What is the ideal mechanical advantage of an inclined plane that is 40 meters long and 8 meters high?
33. In what two ways can a machine alter an input force?
34. What does it mean to say that a machine has a certain mechanical advantage?
35. In which type of lever is the output force smaller than the input force? What benefit is this?
36. Distinguish between ideal mechanical advantage and actual mechanical advantage. How would these compare if a machine were 100% efficient?
37. What is the ideal mechanical advantage for each of the three lever systems shown?
38. A lever is used to lift a heavy load. A 50 N force pushes one end of the lever down 1.2 m, the load rises 0.2 m. Calculate in weight of the load. Neglect friction.
39. (a) When moving a 5000 N piano with a pulley system, the workers note that for every 2 m of rope pulled down, the piano rises 0.4 m. Ideally how much force is required to lift the piano? (b) The workers actually pull with 2500 N of force to lift the piano, what is the efficiency of the pulley system?
40. What are the two main components of mechanical energy?
41. A boulder is raised above the ground so that its potential energy relative to the ground is 20,000 J. It is then dropped. What is its kinetic energy just before it hits the ground?
42. What will be the kinetic energy of an arrow having a potential energy of 50 J after it is shot from a bow?
43. What does it mean to say that in any system, the ‘total energy score’ stays the same?
44. How is energy from coal actually solar energy?
45. How does the amount of work done on an automobile by its engine relate to the energy content of the gasoline?
46. In what way is a machine subject to the law of energy conservation? Is it possible for a machine to multiply energy or work input?
47. What is the efficiency of a machine that requires 100.0 J of input energy to do 35 J of useful work?
48. Most earth satellites follow an oval-shaped (elliptical) path rather than a circular path around the earth. The earth is not at the center of that ellipse so the satellite move closer to and farther from the earth. The PE increases when the satellite moves farther from the earth. According to the law of energy conservation, does a satellite have its greatest speed when it is closest to or farthest from the earth?
49. (a) Why does a small, lightweight car generally have better fuel economy than a big, heavy car? (b) How does a streamlined design improve fuel economy?
50. (a) Does using an automobile's air conditioner while driving increase fuel consumption? (b) What about driving with the lights on? (c) What about playing the car radio when parked with the engine off? Explain in terms of the conservation of energy.
51. You tell your friend that no machine can possibly put out more energy than is put into it, and your friend states that a nuclear reactor puts out more energy than is put into it. What do you say?
52. The energy we require to live comes from the chemically stored potential energy in food, which is transformed into other energy forms during the digestion process. (a) What happens to a person whose combined work and heat output is less than the energy consumed? (b) What happens when the person's work and heat output is greater than the energy consumed? (c) Can an undernourished person perform extra work without extra food? Defend your answers.
53. If a car traveling at 60 km/h will skid 20 m when its brakes lock-up, how far will it skid if it is traveling at 120 km/h when its brakes lock? (Hint: Work Energy theorem)
54. How many kilometers per liter will an SUV get if it is 25% efficient. Assume the SUV is travelling at constant velocity and encounters a constant retarding force of 1000.0 N. The energy content of gasoline is 33,637 kJ/L.
55. Your European friends tell you they are pleased because their new
car gives them 15 kilometers per liter of fuel. Translate this into miles
per gallon so you can decide whether to be impressed. One mile is 1.6 km,
and one gallon is 3.8 liters. Are you impressed?