Download Review Packet for Energy You are pushing a cardboard box across

Review Packet for Energy
1. You are pushing a cardboard box across the floor with friction at constant velocity.
a) Draw a force diagram that contains all of the forces acting on the cardboard box. Assume
real-world conditions (friction, gravity, etc.)
b) Are you doing work on the box? If yes, + or – work? Explain.
c) Is friction doing work on the box? If yes, + or – work? Explain.
d) Is gravity doing work? If yes, + or – work? Explain.
e) What is the net work: +, - , or zero? Explain.
f) If you accelerate the box, is the net work +, - , or zero? Explain.
2. You are carrying your trombone up a flight of stairs. If the stairs are 10 m high how much work
did you do on the trombone by the time you reached the top of the stairs? The trombone has a
mass of 14kg. What is the change in energy? What type of energy changed?
3. You are pushing a 30kg box up a ramp.
a) If the ramp has a vertical height of 3 m how much work did you do on the box?
b) What was its change in energy?
c) If the ramp is 5 m long, how much force did you have to apply?
4. Calculate the velocity of a 5.2 kg object that possesses 26.1 J of kinetic energy.
5. Draw energy bar charts for the following situations:
a) A marble is resting on top of a spring. The spring has been compressed. This initial position
is considered the reference level for the rest of this problem.
b) The spring has been released and the spring extends to its original length. The spring has
launched the marble and the marble has barely left the spring. Hint: what can you assume
about the marble’s velocity at this point?
c) The marble is halfway to its maximum height.
d) The marble has reached its maximum height.
e) Use your energy bar charts to discuss conservation of total mechanical energy.
f) Is this the same as energy is neither created nor destroyed?
6. A car is racing down the highway at 140km/hour. What is the car's kinetic energy?(pay attention
to the given units) The car has a mass of 3000kg.
7. Bart runs up a 2.5 meter high flight of stairs in 9 seconds. If Bart's mass is 65.9 kg, determine
the work which he did and the power he exerted. How many 100W light bulbs can he keep lit?
How long will they stay lit?
8. A car is on the 3rd floor of a 4 story parking lot. The car's mass is 2000kg and each floor is 3 m
high
a) what is the Car’s potential energy with the ground floor as the reference level?
b) What is the Car’s potential energy with the top floor as the reference level?
9. A jumping man reaches a height of 0.5 m off the ground. The man has a mass of 65kg.
a) What is his potential energy at the maximum height of his jump if the ground is the
reference level?
b) What is velocity right just as he leaves the ground (use conservation of energy methods)?
10. Describe a situation in which the total mechanical energy of a system does not change from
start to finish.
11. Draw an energy transformation chart for a CD player hooked up to speakers and turned on. Use
your energy bar chart to discuss conservation of energy as a universal idea.
12. A roller roaster car and passengers of mass 3000 kg is barely moving when it rolls down a 115
m tall hill. The bottom of the hill is the reference level. What is its kinetic energy at the bottom
of the hill? What is its velocity at the bottom of the hill? How much PE grav does it have when
it rolls up the next hill and is 50 m up from the bottom? What is its velocity?