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Work
Energy
Conservation of Energy
Power
100
A rope pulls a bucket up a well. Is the rope doing work on the bucket? If so, is it positive or negative?
Yes- the tension in the rope is causing an upward displacement for the bucket (positive work)
100
Gravitational potential energy is the energy of an object associated with its __________.
Position!
100
True or false: Mechanical energy is always conserved. If true, state your answer. If false, state your answer and correct the statement.
False. Mechanical energy is conserved in the absence of friction.
100
Power is the rate of ___. (Both definitions)
Power is the rate at which work is done. Power is the rate of energy transfer.
200
Ms. Collins pushes as hard as she can against a brick wall. If the wall does not move, has Ms. Collins done any work on the wall? If there was work done, was it positive or negative?
No work was done by Ms. Collins on the wall.
200
If the velocity of a moving object were doubled, by what factor would its kinetic energy increase?
4
200
A ball is dropped from a height of 5.0 m. Neglecting air resistance, what is the velocity of the ball just before it hits the ground?
9.90 m/s
200
How is it possible that the power output of an object can increase but the amount of work that the object does remains the same?
If the amount of time over which the work was done decreased, the power output would increase.
300
For a ball being thrown directly up into the air, is the gravitational force acting on the ball doing work on the ball? If so, is it positive or negative work?
Yes- negative work. The gravitational force is directed downward while the displacement of the ball is upward. This means that the angle between the force and displacement is 180 degrees. cos(180)=-1
300
A spring is compressed a length of 15 cm. If the spring constant is 500 N/m, what is the potential energy stored in the spring?
5.63 J
300
A 8 kg bowling ball is dropped from a certain height above ground. If the bowling ball's velocity just before it hit the ground were 15 m/s and air resistance is disregarded, what potential energy did the bowling ball have before it was dropped?
900 Joules
300
How long does it take a 400 hp engine to do 100,000 J of work?
0.34 s
400
A flight attendant pulls her flight back with a force of 50 N at an angle of 40 degrees above the horizontal over a distance of 500 m. How much work does she do on the flight bag?
19,151.11 Joules
400
A horizontal force of 75 N is applied to a 30 kg box of textbooks as the box is pushed a distance of 5 m across a flat surface. If the box of textbooks started from rest, what is the velocity reached by the textbooks at the end of the 5 m?
5 m/s
400
As an object falls from a certain height, describe what happens to its potential energy, kinetic energy, and mechanical energy.
Potential energy decreases Kinetic energy increases Total mechanical energy remains the same
400
A 50 kg middle school student can pull himself 7 m up a rope in gym class in 25 seconds. What is his power output?
13.73 Watts
500
The rate at which work is done is also known as ___.
Power! (P=W/t)
500
List the units for the following quantities: Potential Energy Kinetic Energy Work Spring Constant Force Displacement
PE- J KE- J W- J k- N/m F- N x/d- m
500
If the net work done on an object it zero, what does this tell you about the object's speed/velocity?
The speed/velocity must remain constant.
500
A 600 kg car accelerates from 2 m/s to 20 m/s in 5 seconds. What was the car's power output?
What is 23,760 Watts