The questions and problems are in the following sections:

Work and Power           (answers to this section)         (back to the top)

1. Define work.

2. Is work done on a car traveling along a straight road at a constant speed?

3. Does the work done in lifting an object up to a given height depend on the speed at which
    it is lifted?

4.  In general, does friction do positive, or negative work on an object in motion?

5.  Cyd uses a horizontal force of 50 N to push a 300 N box across the floor 10 m.

 a)  How much work was done by Cyd?
 b)  Does the normal force do any work on the box?
 c)  If the box moves with constant speed, what is the work done by friction?

7.  Define power.

8.  What is the power of a motor which can do 2000 J of work in 30 sec?
 

 Potential Energy                  (answers to this section)            (back to the top)

1.  What is potential energy?

2.  Give three examples of objects with different types of potential energy.

3.  If the height of an object above the ground is doubled, by what factor does its gravitational
     potential change?

4.  What is the potential energy of a 30 N book sitting on a table top which is 1.5 m above the
     floor and 2.0 m below the ceiling,

 a) relative to the table top?
 b) relative to the floor?
 c) relative to the ceiling?

5.  If a 250 g mouse has a gravitational potential energy of 7.5 J relative to the floor when it is on
     a shelf, how high is the shelf?
 

Kinetic Energy         (answers to this section)         (back to the top)

1.  What is kinetic energy?

2.  If the speed of a car is doubled, by what factor does its kinetic energy change?

3.  You and a friend throw two snowballs straight up into the air.  If you throw yours at twice
     the speed of your friend’s, will yours go twice as high?

4. What is the kinetic energy of a 10 Kg mass moving at 4 m/sec?

5.  If a 45 g golf ball has a kinetic energy of 100 J, what is the speed of the ball?

6.  How fast would a 1000 Kg car have to go to have the same kinetic energy as a 50 g bullet
     traveling at 400 m/s?
 

Change in Energy         (answers to this section)         (back to the top)

1.  A 30 g bullet strikes a tree traveling at 400 m/sec.  If the bullet penetrates 4 cm into the
     tree while stopping, what was the average force exerted on the bullet by the tree?
    What has happened to the energy of the bullet?

2. Two identical bullets are placed into a hand gun and a rifle.  Will they exit the guns at the
    same speed?  Explain.

3.  If you are going 25 mph through a school zone when you should be moving at 15 mph,
     how much farther will it take you to stop?

4. An elevator is stopped at the 4th floor.  It descends and stops at the 2nd floor.

 a) Does the total energy of the elevator change in going from the 4th floor to the 2nd?
 b) If the energy changes, where does the energy go?

5. An unsupported object falls due to the force of gravity.

 a) Is the gravitational force considered an internal or an external force?
 b) does the total energy of the object change as it falls?  (neglect friction)

a) did the kinetic energy of the ball change?
b)  If so, what did work on the ball?
c)  How does the strength of the batter and follow through affect the outcome of the hit?

7.  A force of 500 N is applied to a 200 Kg object for a distance of 3 m.  What is the change
     in kinetic energy of the object if the object does not change its height?

8.  A 0.2 Kg ball falls from a 1.2 m high table to the floor.  How much potential energy was
     lost by the ball?

9.  A student lifts a 15 Kg box from the floor to a shelf 2 m high.  How much work did the
     student do?

10.  If it takes an average force of 16 N to push a 20 g dart 8.0 cm into the “loaded” position
       in a dart gun, how fast will the dart be going when it exits the gun?

11.  A 44 Kw motor requires 20 sec to pull a 3000 Kg roller coaster train to the top of the
      first hill.  If the speed of the train at the top of the hill can be ignored, how high is the hill?

12.  How much power is required to throw a 300 g baseball at 30 m/s, starting from rest, in 0.75 sec?
 

Conservation of Energy       (answers to this section)         (back to the top)

1.  A car skids off of the road, strikes a tree head-on, and comes to rest.  Was the kinetic
     energy of the car conserved?  If not, where did the energy go?

2.  Describe where the maximum and minimum potential and kinetic energies occur for a
     swinging pendulum.

3.  You and your smaller cousin each sit in identical swings at the park.  If you both start from
     the same angular displacement, which of you, if either, will be moving faster at the bottom
     of the swing’s arc?

4.  Use energy concepts to calculate the speed of a rock after it has fallen 0.5 m from rest.

5.  If the fastest you can throw a ball is 30 m/s, what is the highest the ball can go if you throw
     it straight up?

6.  While watering the lawn you notice that the water can go 12 m into the air when you point
     the hose straight up.  How fast is the water coming out of the hose?

7.  The top hill on a roller coaster is 35 m above the ground.  If the bottom of the first hill is at
     ground level,

 a)  what is the speed of the train at the bottom of the hill?  (the small speed of the train
      at the top of the first hill can be ignored)
 b)  would a train full of riders go at a different speed than an empty train?
 c)  if the train continues and goes to the top of the next hill which is 15 m above the
     ground, what is the speed of the train as it passes over the second hill?

9.  The first hill of the Demon is 20 m above the ground and the top of the first loop is 12 m
     above the ground.  If the train goes through the loop at 10.0 m/s, what percentage of the
     train’s energy was lost to friction before getting to the top of the loop?  (the small speed of
     the train at the top of the first hill can be ignored)

10.  A .3 Kg rubber ball falls 2.5 meters to the floor and rebounds to a height of 2.1 m.

 a)  What percentage of the ball’s total energy is missing?
 b)  Where did that energy go?
 c)  If the ball loses the same percentage of energy on each bounce, what height will
      the ball reach after the third bounce?