Define power, including the equation to calculate power.
The rate at which work is done.
Power = work done/time interval
100
Define potential energy and provide the formula to calculate.
PE is the energy an object has because of its location.
(Stored energy)
PE = mgh
100
Define kinetic energy and provide the equation for solving
Kinetic energy is the energy of motion.
KE = 1/2m X v^2
100
According to the law of conservation of energy, a bouncy ball should never stop bouncing. But, we saw that it does! Where does the energy go then?
Some of the energy gets converted to sound energy and some to thermal energy.
200
What is the difference in work if you carry a 10 kg box up two flights of stairs, compared to carrying the same box up one flight of stairs?
Twice as much work is required to lift the same load twice the distance.
200
What is the unit for power?
Watt
200
Which of the following is the best example of increasing an object's PE?
A) Stretching a rubber band
B) Dropping a rubber band
C) Shooting a rubber band across the room
A) Stretching a rubber band
200
If an object has kinetic energy, then which of the following will it also have?
A) Force
B) impulse
C) momentum
D) acceleration
C) Momentum (m x v)
200
In terms of a swinging pendulum, describe the following:
Point (s) where the PE is the greatest
Point (s) where the KE is the greatest
PE is greatest at the end points of its swing. (top)
KE is greatest at the lowest point of its swing.
300
What is the ratio of useful work output to total work input called?
Efficiency
300
How much power is required to do 100 J of work in 10 s?
Power = work/time
= 100 J / 10 s
= 10 W
300
Which is the amount of PE possessed by an elevated object is equal to?
A) Power to lift it
B) Distance lifted
C) Work done in lifting it
D) Force needed to lift it
C) Work done in lifting it
300
A car moves with a kinetic energy of 1000J. If its speed doubles, what will it kinetic energy be?
KE = 1/2 m X 2 v^2
KE is increased by 4 due to v^2.
KE = 4000J
300
Rockets are launched from a airplane in the forward direction of motion. How will the launch impact the KE of the airplane?
The KE of the airplane will decrease.
400
Two people with the same mass carry a 2 kg load up a flight of stairs. The first person climbs the stairs in 30s, while the other climbs them in 40s. Which person does more work, and which person uses more power?
Work is the same! Climber in 30s uses more power due to shorter time.
400
Which requires more power, carrying 50 N slowly up a flight of stairs, or carrying the same load quickly up the stairs?
More power is required for a shorter time, so carrying quickly will require more power.
400
What is the PE possessed by a 1 kg book when it is elevated 4 m?
PE = mgh
1 kg X 10 m/s^2 X 4 m = 40J
400
What change in kinetic energy does an airplane experience on takeoff if it is moved a distance of 500 m by a sustained net force of 5000N?
Change in KE = Fd
= 5000N X 500m
= 2,500,000 J = 2.5MJ
400
A stuntman jumps from a cliff, starting with 10,000 J of PE. Show his PE and KE at the midway point, 3/4 of the way down, and right before he hits the ground.
Midway: PE & KE both are 5,000J
3/4: PE = 2500 KE = 7500
Bottom: PE = 0 KE = 10000J
500
What is the work done to lift 100 kg of blocks to a height of 2 meters?
W = Fd = (100 kg X 10 m/s^2) X 2 m = 2000 J
500
Calculate the power expended when a 20-N force pushes a cart 3.5 m in a time of .5 s.
Power = W/t = (20 N X 3.5 m) /.5s = 140 W
500
Calculate the height of a table if 100 J of energy is required to lift a 1 kg book from the floor to rest on the table.
Given: PE = 100J
m = 1 kg
g = 10 m/s^2
PE = mgh
Rearrange to solve for height: h = PE/mg
Solve: h = 100J/(1kg X 10 m/s^2)
Solution: 10 meters
500
A 50 N object moves at 1 m/s. Calculate its kinetic energy.
Givens:
Force = 50 N
Velocity = 1 m/s
Unknown: KE
KE = 1/2 m x v^2
Must first get the mass: F=mg Rearrange to solve for m
m = F/g = 50N/10m/s^2 = 5 kg
Solve: (.5 x 5 kg) x (1 m/s)^2
Solution: 2.5 J
500
When two balls on one end of Newton's cradle are elevated and released, two balls on the other end will pop out. If instead, only one ball popped out but had twice the speed, which conservation law(s) would be violated?