Concepts
Think and Rank
Plug and Chug
Think and Explain
Think and Solve
100
A force sets an object in motion. When the force is multiplied by the time of its application, we call the quantity impulse, which changes the momentum of that object. What do we call the quantity forcexdistance, and what quantity can this change?
Work The objects energy
100
Car A: v=1.0m/s, m=800 kg Car B: v=2.0m/s, m=1000 kg Car C: v=8.0m/s, m=90 kg The mass and speed of three cars is shown. Rank by momentum from greatest to least.
B,A,C
100
How much power is required to do 100 J of work on an object in a time of 0.5 s? How much power is required if the same work is done in 1 s?
200W 100W
100
Which requires more work: stretching a strong spring a certain distance or stretching a weak spring the same distance? Defend your answer
More force is needed to stretch a strong spring so more work is needed in stretching the same distance.
100
A stuntman on a cliff has a PE of 10,000 J. Show that when his potential energy is 2000 J, his kinetic energy is 8000 J
8000 J
200
Work is required to lift a barbell. How many times more work is required to lift the barbell three times as high?
3
200
Car A: v=1.0m/s, m=800 kg Car B: v=2.0m/s, m=1000 kg Car C: v=8.0m/s, m=90 kg The mass and speed of three cars is shown. Rank by KE from greatest to least.
C,B,A
200
If you do 100 J of work to elevate a bucket of water, what is its gravitational potential energy relative to its starting position?
100 J
200
Two people who weigh the same amount climb a flight of stairs. The first person climbs the stairs in 30 s, while the second person climbs them in 40 s. Which person does more work? Which uses more power?
Work is the same the 30s climber uses more power
200
Relative to the ground below, how many joules of PE does a 1000-N boulder have at the top of a 5-m ledge? If it falls, with how much KE will it strike the ground? What will be its speed on impact?
10 m/s
300
What are the two main forms of mechanical energy?
PE and KE
300
Consider these four situations. (A) a 3-kg ball at rest atop a 5-m-tall hill (B) a 4-kg ball at rest atop a 5-m-tall hill (C) a 3-kg ball moving at 2 m/s atop a 5-m-tall hill (D) a 4-kg ball moving at 2 m/s at ground level Rank from greatest to least the potential energy of each ball.
B, A=C, D
300
Calculate the work done when a 20-N force pushes a cart 3.5 m
1100 J
300
Consider the kinetic energy of a fly in the cabin of a fast-moving train. Does it have the same or different kinetic energies relative to the train? Relative to the ground outside?
Different because motion (speed) is also relative
300
A hammer falls off a rooftop and strikes the ground with a certain KE. If it fell from a roof that was four times higher, how would its KE of impact compare? Its speed of impact? (Neglect air resistance.)
4 times as much
400
A boulder is raised above the ground so that its potential energy relative to the ground is 200 J. Then it is dropped. What is its kinetic energy just before it hits the ground?
200J
400
Consider these four situations. (A) a 3-kg ball at rest atop a 5-m-tall hill (B) a 4-kg ball at rest atop a 5-m-tall hill (C) a 3-kg ball moving at 2 m/s atop a 5-m-tall hill (D) a 4-kg ball moving at 2 m/s at ground level Rank from greatest to least the kinetic energy of each ball.
D,C,A=B
400
Calculate the power expended when a 20-N force pushes a cart 3.5 m in a time of 0.5 s
140 W
400
In what two ways can a machine alter an input force?
magnitude and or direction
400
A car can go from 0 to 100 km/h in 10 s. If the engine delivered twice the power, how many seconds would it take?
5 s
500
Suppose you know the amount of work the brakes of a car must do to stop a car at a given speed. How much work must they do to stop a car that is moving four times as fast? How will the stopping distances compare?
16 times as much work 16 times as much distance
500
Rank the efficiency of these machines from highest to lowest. (A) energy in 100 J; energy out 60 J (B) energy in 100 J; energy out 50 J (C) energy in 200 J; energy out 80 J (D) energy in 200 J; energy out 120 J
A=D, B,C
500
Calculate the number of joules of kinetic energy a 1-kg book has when tossed across the room at a speed of 2 m/s.
2 J
500
In what way is a machine subject to the law of energy conservation? Is it possible for a machine to multiply energy or work input?
Work in can not exceed work output
500
If a car traveling at 60 km/h will skid 20 m when its brakes lock, how far will it skid if it is traveling at 120 km/h when its brakes lock? (This question is typical on some driver’s license exams.)
80 m
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