WS #7 - Energy & Momentum Study Guide (CP)
Equations given on test:
KEi + PEgi + PEsi +Eadd = KEf + PEgf + PEsf + Elost 1HP = 746W
KE = ½ mv2 PEg = mgy PEs = ½ kx2 W = F x d Fr = mN
Smvbefore = Smvafter V1i –V2i = -(V1f – V2f)
1. Energy is the ability to do what?
2. Using the impulse-momentum theory, explain why when jumping from a high height, it is better to bend your knees as you land instead of landing with your knees locked.
3. A 75 kg stunt man jumps from a 15 m building and lands safely in a large air mattress.
a. How much potential energy does he have at the top of the building?
b. Where does all his energy go when he lands and comes to a stop?
c. If the air mattress compresses 5 m, what is the force on the stunt man from the mattress?
4. A worker pulls a 40.0-kg crate with a rope at a 30.0o angle to the horizontal using a 55.0 N force. He moves the crate a distance of 7.00 m while a frictional force of 35.0 N acts on the crate.
a. How much work does the worker do on the crate?
b. How much work does friction do on the crate?
c. How much work does gravity do on the crate?
d. How much work does the normal force do on the crate?
e. What is the net work done on the crate?
5. A 20.0 kg crate at rest on a 10.0 m high ramp, requires a 100. J push to get it moving down the ramp. The ramp and crate experience 20.0 J of friction. What is the kinetic energy of the block at the bottom of the ramp?
6. A spring sitting on top of a 2.0 m high counter has a spring constant of 450 N/m. A 5.5 kg block is held at rest against the spring, compressing the spring 0.22 m. If the block is then let go, what is the block’s final velocity right before it hits the floor?
7. A 2.5 –g (0.0025 kg) bullet traveling at 350 m/s hits a tree and slows uniformly to a stop while penetrating a distance of 12 cm into the tree’s trunk. What force was exerted on the bullet in bringing it to rest?
8. A 150-g baseball reaches a batter with a speed of 25 m/s. After it has been struck, it leaves the bat at 35 m/s in the opposite direction. If the ball was in contact with the bat for .001 s, find the average force exerted on it during this period.
9. A 35 g ball hits a wall at 10.0 m/s. It bounces off the wall with a speed of 8.0 m/s and the ball is in contact with the wall for 0.20 s, what is the average force exerted by the wall on the ball?
10. A 30.0 kg girl who is running at 3.0 m/s jumps on a stationary 10.0 kg sled on a frozen lake. How fast does the sled move with the girl on it?
11. A 0.50 kg clay ball rolls down a 0.30 m ramp.
a. What is the velocity of the ball at the bottom of the ramp?
b. Then the ball rolls across a level table where it collides inelastically with a stationary toy car of mass 1.5 kg. What is the velocity of the clay-car combo?
c. The clay-car combo then falls off the 1.25 m high table. What is the velocity of the clay-car combo just before it hits the floor?