Motion and Force Chapter 4 Study Guide
Write the definition, equation, and units used for each of the following vocabulary words
Term / Definition / Equation / UnitsWork / The use of force to move an object some distance / Work = Force . distance / Joules (J)
Potential Energy / Stored energy; the energy an object has due to its position or its shape / GPE = mass . gravitational acceleration . height
GPE = mgh (g = 9.8 m/s2) / Joules (J)
Kinetic Energy / The energy of motion / KE = 0.5 . m . v2 / Joules (J)
Mechanical Energy / An object’s combined potential and kinetic energy. / ME = KE + PE / Joules (J)
Power / The rate at which you do work. / Power = work / time
Power = energy / time / Watts
(W)
1. Give an example of doing work A person pushing a book across a floor
2. Without increasing mass, how could you increase the potential energy of an object? Increase the height of the object
3. Two vehicles have the same velocity but different masses. The vehicle with greater mass will have more Kinetic Energy.
4. You transfer energy to an object when you do work on it.
5. The power to use a curling iron increases when you switch it from low heat to high heat.
6. When you push on a wall with all of your strength but the wall doesn’t move, are you using force and/or
work? Explain. You use force, but you do not do any work on the wall because it doesn’t move.
7. A wagon rolling down a hill has a kinetic energy of 600 J and a potential energy of 4780 J. What is the wagons mechanical energy? (please show all of your work) 5380 J
8. Define the law of conservation of energy no matter how energy is transferred or transformed, all of the energy is still present in one form or another.
9. Relate the law of conservation of energy to the amount of mechanical energy a skier has at the top of a hill
compared to the bottom of a hill. Due to the law of conservation of energy the skier will have the same mechanical energy at the top of the hill as the bottom of the hill, however the amount of PE and KE will change. The skier will have great PE at the top of the hill and greater KE at the bottom of the hill
10. If a skater does a flip off of a ramp then the skater has what type(s) of energy while in the air? Both Kinetic and Potential Energy
11. Kelly applies a 300 N force for 15 s to slide a box 5 m across the floor. What is Kelly’s power? 100 W
12. In order to increase work done in a given amount of time you need to increase power.
13. The power an appliance needs depends upon the rate at which it uses energy.
14. Sam holds a 7 kg ball over his head at a height of 3 m. What is the gravitational potential energy of the ball? 205.8 J
15. Meg has a mass of 75 kg. When she rides her bike at a velocity of 5 m/s, what is her kinetic energy? 937.5 J
Answer the following questions on a separate sheet of paper
16. Jack and Hunter each exert 150 N to lift identical boxes 2 m. Jack lifts his box twice as fast as Hunter does. How do their work and power compare? (terms to use: force, distance, and time)
Jack and Hunter use the same force to lift the box the same distance so their force is the same. Jack lifts his box twice as fast as Hunter so Jack’s power is twice as much as Hunters.
17. Sarah is pulling a wagon by its handle. The handle is not level with the ground but is being pulled upward as well as forward. Does all of Sarah’s force do work on the wagon? Explain.
Not all of the force Sarah applies to the handle does work. Sarah pulls the wagon at an angle so only some of the force is applied in the same direction as the wagon. Only the part of the force that is applied in the same direction that the wagon moves does work.
18. Describe your motion when you are on a swing in terms of kinetic energy and potential energy. At which point during your motion is each type of energy greatest? Tell why you need a push occasionally to keep you going. (terms to use: PE, KE, air resistance, ME, and friction)
When I am on a swing, my energy changes from greatest potential energy at the top of my swing (both sides) to kinetic energy throughout the swing. Potential energy is greatest at the top of each swing. Kinetic energy is greatest at the bottom. I need a push once in a while because energy is lost to air resistance, and to the fiction in the rope or chain as it rubs on the supporting bar.