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Review for Unit 5 Test
Use this review as a GUIDE for studying. Remember to study the notes as well as your
Work & Power Quiz and Energy Quiz
1. Define the following terms
The ability to do work
Energy
Energy of motion
Kinetic Energy
Stored energy/energy due to position
Potential Energy
Force applied over a distance
Work
Rate at which work is done
Power
Says energy cannot be created or destroyed, but can
Law of Conservation change forms
of Energy
Change of forms (ex. Mechanical to heat by rubbing
Energy hands together)
Transformation
Movement of energy from one object to another (ex.
Energy Transfer Convection, conduction, radiation)
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2. List the equations and units for the following
Equation(s)
Unit(s)
Joule = J (N-m)
Work
W=Fxd
F = force (N), d = distance (m)
P = W/t
W = Work (J), t = time (s)
Watt = W (J/s)
Power
KE = ½ m v2
m = mass (kg), v = velocity (m/s)
J (N-m)
Kinetic Energy
PE = mgh or wh
Potential Energy
m = mass (kg), g = 9.8 m/s2, h = height (m),
(2 equations!)
w = weight (N)
Velocity
(using KE)
V = √(2KE/m)
KE = Kinetic Energy (J), m = mass (kg)
J (N-m)
Meters/Second =
m/s
3. Identify the relationship between the following as being inversely or directly
proportional.
Proportional (Circle One)
Inversely
Directly
Work and Force
Work and Distance
Power and Work
Power and Distance
Power and Force
Power and Time
PE and Mass
PE and Height
KE and Mass
KE and Speed
Inversely
Directly
Inversely
Directly
Inversely
Directly
Inversely
Directly
Inversely
Directly
Inversely
Directly
Inversely
Directly
Inversely
Directly
Inversely
Directly
4. Give at least one example of one object that has each of the following types of
energy
Object(s)
Electrical Toaster, TV, etc (anything that plugs in)
Mechanical
Motion energy (Fan, Ball at top of hill)
Mostly associated w/ potential & kinetic
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Chemical
Battery, food, etc
Solar
Sun
Light
Light bulb, TV, Computer, Toaster, etc
Sound
Stereo, TV, etc
Nuclear
Nuclear power plant
Elastic
Rubber band, springs, etc
5. Give at least one example of an object that has the following energy transformations.
Object(s)
Electrical to Mechanical
Fan
Mechanical to Electrical
Windmill
Electrical to Heat
Toaster, hair dryer, etc
Chemical to Light
Glow Stick, Glow Necklace
Chemical to Electrical
Flashlight
Electrical to Sound
Radio, TV
Solar to Electrical
Elastic (Potential) to Kinetic
Solar Panels
Jack in the Box
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5. 100 J of energy is put into a system. 68 J comes out of the system as
mechanical energy. How much was “lost” to heat energy?
32 J (Law of conservation of energy- cannot lose or destroy energy, what goes in must
come out)
6. As an object falls, what happens to the potential energy? Kinetic energy?
PE decreases (height decreases), KE increases (velocity/speed increases)
7. If you push on a wall and it doesn’t move, you are not doing work on the wall.
Why?
No distance covered
8. What has to be true about force and distance in order for work to be done?
Must be in the same direction
9. Does KE depend more on speed or mass? Why?
Speed- b/c in the equation you use velocity squared
10. Calculate the work and power when lifting a 50 kg bag to a height of 5 m in a
time of 2 seconds.
W = F x d = 490 N x 5 m = 2450 J
50 g x 9.8 m/s/s
P = W/t = 2450 J/ 2 s = 1225 W
= 490 N
11. If a father lifts his child 2.3 m into the air and exerts a force of 210 N, what is the
work done by the dad?
W = F x d = 210 N x 2.3 m = 483 J
12. The dad lifts the child (#16) in 4 seconds. What is his power?
P = W/t = 483 J/4s = 120.75 W
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13. If the dad lifted the child in half the time, how would the new power compare to the
original? What about if he lifted the child in twice the amount of time? (Hint: say if
the power increases or decreases and also by how much!)
Half the time: Power would increase by factor of 2 (inversely proportional)
Double the time: Power would decrease by factor of 2
14. A moving car has kinetic energy. If it speeds up until it is going 3 times the original
speed, how much kinetic energy does it have compared to the original?
Since KE = ½ mv2, KE is directly proportional to v2, which means KE would increase by
factor of 9.
15. A dog is traveling at 3 m/s. If the mass of the dog is 30 kg, what is the KE of the
dog?
KE = ½ mv2 = ½ (30 kg)(3 m/s)2 = 135 J
16. What is the potential energy of a 120 lbs skier at the top of a 400 m mountain?
PE = mgh = 54.55 kg x 9.8 m/s2 x 400 m = 213,818 J
Mass = 120 lbs x 1 kg
= 54.55 kg
2.2 lbs
17. What is the mass (kg) of an object that has a potential energy of 25.5 J at a height
of 2.4 ft?
m = PE =
25.5 J
= 3.56 kg
gh
(9.8m/s2 x 0.732 m)
h = 2.4 ft x 1 m
= 0.732 m
3.28 m
18.
A cheetah has an average weight of 110 lbs and an average kinetic energy of
7998 J. What is the average speed of a cheetah?
v = √(2KE/m) = √(2 x 7998 J / 50 kg) = 17.89 m/s
m = 110 lbs x 1 kg
2.2 lbs
= 50 kg
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19. A constant force of 240 N is exerted on a box to move it across the floor. If 1800 J
of work is done on the box, how far did the box move?
d = W/F = 1800 J / 240 N = 7.5 m
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