Download Answer all questions on a separate piece of paper.

Sierzega/Ferri: Energy 7
Review
Answer all questions on a separate piece of paper.
7.1 Calculate the gravitational potential energy in the following systems (Earth is included in all cases):
a. A car with a mass of 1200 kg at the top of a 42 m high hill.
b. A 65 kg climber on top of Mount Everest (8800 m high).
c. A 0.52 kg bird flying at an altitude of 550 m.
d. A science student holds a 55 g egg out a window. Just before the student releases the egg, the eggEarth system has 8.0 J of gravitational potential energy with respect to the ground. How far is the
student’s arm from the ground in meters?
55 g = ________ kg
7.2 Calculate the kinetic energy in the following systems:
a. A car with a mass of 900 kg moving at a speed of 22 m/s.
b. A 65 kg sprinter moving at a speed of 5 m/s.
7.3 Calculate the velocity of the following objects:
a. A 30 kg car with 1200 J of kinetic energy.
b. A 24 kg child with 800 J of kinetic energy.
7.4 You lift a heavy suitcase at a constant velocity from the floor to the top shelf of the closet expending
power of 200 W in 3 seconds.
a. Draw before and after sketches and a bar chart. The system is the suitcase and Earth.
b. How much work is done to lift the suitcase?
c. What is the force exerted on the suitcase?
d. If the suitcase’s mass is 30 kg, what is the height to which the suitcase is raised?
Sierzega/Ferri: Energy 7
7.5 Represent and Reason
Dylan sleds down a hill and then travels for some distance on the snow until he stops. Represent the
following processes with bar charts. Identify all of the objects included in your system and your
reference level.
a) Initial state: Dylan and sled on top of a mountain; final state: Dylan and sled are 1/3 of the way
down the mountain and moving;
b) Initial state: Dylan and sled are 1/3 of the way down the mountain and moving; final state: Dylan
and sled moving fast at the bottom of the mountain;
c) Initial state: Dylan and sled moving fast at the bottom of the mountain; final state: Dylan and
sled stop after traveling for some time on a horizontal surface.
d) Is energy still conserved even though Dylan came to rest? How do you know?
7.6 Fill in the table that follows.
Experiment: Describe the
system and process.
A motor pulls a roller
coaster up the first hill of
the track via a chain.
Initial state: The roller
coaster is at rest at the
bottom of the hill.
Final state: The roller
coaster is moving at a
moderate speed at the top
of the hill.
System: Includes the
roller coaster, chain, and
Earth but excludes the
motor that pulls the chain
up the hill.
Draw a sketch showing
the initial and final states.
Circle the object(s) in the
system.
Construct a work-energy bar chart and write
the equation below.
Sierzega/Ferri: Energy 7
7.7 Repeat the previous activity with a different system.
Experiment: Describe the
system and process.
Draw a sketch showing
the initial and final states.
Circle the object(s) in the
system.
Construct a work-energy bar chart and write
the equation below.
System: Includes the
roller coaster and the
chain but excludes Earth
and the motor that pulls
the chain up the hill.
7.8 Describe a real-life situation in which an external force does the following and state explicitly
whether the system’s energy increases or decreases:
a) Positive work on a system;
b) Positive work on a system but with a value that is less than in part (a);
c) Negative work on a system;
d) Zero work on the system even though an object in the system moves.
7.9 Draw sketches of 3 processes in which the energy of a system changes as external work is done on
the system. Then give your sketches to your friend who will draw bar charts to represent the processes.
You, in turn will draw bar charts for her/his processes. After both are done, exchange your bar charts.
Did you friend represent your ideas correctly? Did you?
7.10 Katie pushes a shopping cart down a 10 m aisle by exerting a constant force of 12 N. The cart
moves with a constant velocity of 1 m/s. Draw a motion and a force diagram for the cart. Create a workenergy bar chart that is consistent with the situation. Notice that the speed of the cart is constant
although Katie is exerting a constant force on it.
Sierzega/Ferri: Energy 7
7.11
Madison pushes a square block across a rough surface.
The block moves with constant velocity. The surfaces of
the block and the floor become warmer.
Draw a motion diagram and a force diagram for the block.
a) Consider the block and the floor in the system.
Does Madison do work on the
system? Explain your answer.
Does the floor do work on the
system? Explain your answer.
Draw a work-energy bar
chart.
b) Consider just the block in the system.
Does Madison do work on
the system? Explain your
answer.
Does the floor do work on the
system? Explain your answer.
Draw a work-energy bar
chart.
c) Describe the difference between the two situations described above. Is one of these systems
better than the other?
Sierzega/Ferri: Energy 7
FEarth on Object = mg
W = Work (J)
W = Fd
F = Force (N)
Ug = mgh
∆x = Displacement (m)
K = ½mv2
Ug = Gravitational Potential Energy (J)
P=
W DU
=
Dt Dt
g = 10 N/kg
K = Kinetic Energy (J)
h = height (m)
P = Power (W)
∆t = time (s)
m = mass (kg)
g = acceleration due to the pull of the Earth