Download 40m 20 N

Name: _________________________________
GP: Work, Power & Energy
AP Physics – McNutt
Date: ___________ Period: __________
Conservation of Energy Review
Solve the problems using appropriate equations and provide all units.
1.) 50 kg gymnast comes to a stop after tumbling. Her feet do 10,000 J of work to stop her. What was
the girl's velocity when she began to stop?
Formula & Givens
Input Numbers & Show Your Work
Solution
Rearrange
KE = ½ mv2 =
20m/s
KE = ½ mv2
v2 = KE/ ½ m = 10,000J / ½ (50kg)
M = 50kg
= 10,000/25 = 400 sqrt 400 = 20m/s
KE = 10,000J
2.) A 20-N force is exerted on a box, moving it 40 m in the same direction.
What is the magnitude of work done on the box?
20 N
40m
Formula & Givens
Input Numbers & Show Your Work
Solution
W=Fxd
W= (20-N)(40m) = 800J
800J
F = 20 N
D =40m
3.) Conveyor belts are often used to move packages around warehouses. A conveyor moves packages
at a steady 4.0 m/s. A 500N employee decides to catch a ride by sitting on a 1,000 N box for a 50 m
trip: What is the work done by the employee on the box?
Formula & Givens
Input Numbers & Show Your Work
Solution
Ha! Gotcha! This is a
The employee is doing no work, man, he’s just
Your answer is 0
trick question…
hitching a ride on the box. The conveyor belt is
doing all the work.
4.) A 1,000 kg car is initially at rest. The engine starts and provides 10,000 J of work on the car. What
is the final velocity of the car?
Formula & Givens
Input Numbers & Show Your Work
Solution
KE = 1/2mv2
KE = 1/2mv2
(10,000 J) = ½(1,000kg) v2
2.236 m/s
v2 = (10,000 J) / ½(1,000kg) = 10,000J/2000
v2 = 5 → √5 = 2.236 m/s
5.) A power-lifter raises a 1,000 N weight a distance of 2.0 meters in 0.5 seconds, what is his power
output?
Formula & Givens
Input Numbers & Show Your Work
Solution
W=Fd
P = (1000-N)(2.0m)/0.5s = 4000 Watts
4000 Watts
P = W/t
6.) According to the Law of Conservation of Energy, we cannot create new energy. We can, however,
convert find new ways to convert energy into usable forms and energy in less time to increase power.
Provide an example of how we do both of the above.
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7.) Calculate the potential energy of a 6 kg bowling ball suspended 3 m above the surface of the Earth.
Formula & Givens
Input Numbers & Show Your Work
Solution
PE = mgh
PE = (6kg)(9.8)(3m) = 176.4J
176.4J
8.) A tennis ball launcher works by using a spring to propel the ball forward as shown below:
One model of tennis ball launcher has advertised that it is capable of imparting 15,000 J of kinetic
energy to a 0.5 kg ball initially at rest. A student carefully measures the compression of the spring to
be 0.10 m. What is the elastic energy stored in the spring?
Formula & Givens
Input Numbers & Show Your Work
Solution
PE1 + KE1 = PE2 + KE2
k = spring constant
x = 0.10m
KE = 15,000 J
9.) What is the value of the spring constant for the tennis ball launcher according to the data provided?
Formula & Givens
Input Numbers & Show Your Work
Force = F = kx
F = load applied on
the spring = mg
m = 0.5 kg
g = 9.8 m/sec^2
k = spring constant
x = 0.10 m
Force = F = kx
Solution