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.
100
Newton's Second Law
F = ma
200
Collin pushes as hard as he can against a brick wall. If the wall does not move, has Collin done any work on the wall? If there was work done, was it positive or negative?
No work was done by Collin 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?
10 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.
200
Friction between two objects that are not moving.
Static Friction
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.
300
Definition of Energy
The ability to do work
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? (Note 1Hp = 745W)
0.34 s
300
What happens to the normal force of an object on an incline, if the the angle of the incline is increasing?
Normal force decreases.
400
A flight attendant picks up a 15kg bag to put in the over head compartment. If the over head compartment is 2.5m off the ground, how much work has the flight attendant done.
375 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? (Assume he moves with constant velocity)
140 Watts
400
What is the equation for the component of the gravitational force of an object on an incline
mgsin(theta)
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
Force
Displacement
PE- J
KE- J
W- J
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
500
If a 75kg sky diver falls out of an airplane and feels a force of air resistance of 400N, what is the sky divers acceleration?