Work and Power
Potential Energy
Kinetic Energy
Conservation of Energy
Other
100
A 20 N force moves a book through a certain distance, performing 40 J of work in the process. How far did the book move?
2 m
100
Relative to the ground below, what is the gravitational potential energy of a 100 kg boulder that is on the top of a 5-m ledge?
5000 J
100
What is the kinetic energy of a 4-kg cart that is moving at 5 m/s?
50 J
100
A popper has 50 J of elastic potential energy. Assuming no loss of energy to heat, sound or air friction, how much kinetic energy will it have when it comes back down to the table?
50 J
100
What are the SI units of work? What are the SI units of energy? What are the SI units of power?
J, J, W
200
Which requires more work, lifting a 10 kg load a vertical distance of 2 m or lifting a 5 kg load a vertical distance of 4 m?
Same amount of work
200
Name three kinds of potential energy and an example of where you can find them.
elastic - rubberbands, springs chemical - batteries, food, fossil fuels gravitational - due to elevation/height
200
Suppose a moving car has 2000 J of kinetic energy. If the car's speed triples, how much kinetic energy will it then have?
18,000 J
200
A person on a roof throws one ball downward and an identical ball upward at the same speed. The ball thrown downward hits the ground with 70 J of kinetic energy. Ignoring air friction, with how much kinetic energy does the second ball hit the ground? a. less than 70 J b.70 J c. 140 J d. more than 140 J
b. 70 J
200
A ball is thrown into the air with 50 J of kinetic energy, which is transformed to gravitational potential energy at the top of its trajectory. When it returns to its original level after encountering air resistance, its kinetic energy is a. more than 50 J. b. 50 J. c. less than 50 J. d. Not enough information given.
c. Less than 50 J
300
Two people who weigh the same amount climb a flight of stairs. The first person climbs the stairs in 30 seconds, while the second person climbs them in 40 seconds. Which person does more work? Which uses more power?
same work, 30 seconds is more power
300
The amount of potential energy possessed by an elevated object is equal to: a. the power used to lift it. b. the distance it is lifted. c. the force needed to lift it. d. the work done in lifting it. e. the value of the acceleration due to gravity.
d. the work done in lifting it.
300
Suppose a car takes 15 m to stop when it is going 20 m/s. How far will it take to stop it if it is going 40 m/s?
60 m
300
Consider the bar graph pictured. Where on the track could the skater be?
(bar graph posted on board and answer on board)
300
In the Skatepark lab, what effect did the mass have on the total energy of the system?
energy increases with mass because you give it an initial PE = mgh
400
A car can go from 0 to 100 km/hr in 10 seconds. If the engine delivered twice the power, how many seconds would it take?
5 seconds
400
If you do 100 J of work to elevate a bucket of water, what is its gravitational potential energy relative to its starting position? What would be the gravitational potential energy if the bucket were raised twice as high?
100 J, 200 J
400
Consider molecules of hydrogen gas and molecules of heavier oxygen gas that have the same kinetic energy. Which molecules have the greater speed?
hydrogen
400
Consider the picture of a rollercoaster drawn on the board. The car is at rest at point A. Rank the speeds from greatest to least.
D, B, C, E, A
400
How much work is required to stop a 50-kg bike moving at 10 m/s?
2500 J
500
Calculate the power expended when a force of 5 N moves a book 2 m in a time interval of 4 seconds.
2.5 W
500
If someone lifts a 2 kg book up 1.5 meters, what is its gravitational potential energy relative to its starting position?
30 J
500
The mass and speed of three vehicles is listed below. Rank the vehicles by kinetic energy from greatest to least. (a) 800 kg car moving 10 m/s (b) 1000 kg car moving 20 m/s (c) 90 kg bike moving 80 m/s
c (288,000 J), b (200,000J) then a (40,000 J)
500
A stuntman on a cliff has a PE of 10,000 J (relative to the ground below). (a) How much kinetic energy does he have when his potential energy is 2000 J? (b) Is he less than halfway down, halfway down, or more than halfway down at this point?
a - 8000 J b - more than halfway down
500
Draw a bar graph representing all the different types of energy (include a bar for total energy) for the following situation: A skateboarder is at the bottom of the ramp, zooming past the middle. Do not neglect friction.
answer on board
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