Download Energy and momentum Extra Examples - Ms. Gamm

A.P. Physics - B
Unit 3
Work, Energy, and Momentum
Extra Example Problems
1. A 70 kg person descends in an elevator at a constant speed of 4 m/s, covering a distance of 20
meters.
a. What is the work done by gravity on the person during this descent?
b. What is the work done by normal force on the person during this descent?
c. What is the net work done on the person during this descent?
2. A 4 kg box sliding across a horizontal frictionless surface is initially moving at 5 m/s, when a
forward applied force of 10 N begins acting on the box. How fast is the box moving at the end of
5 meters of motion with the applied force acting? (Use ideas from this unit.)
3. A box is started from the top of a frictionless incline, where it is given a push so that it starts
moving down the incline at a speed of 7.2 m/s. If the top of the incline is 95 cm higher than the
base of the incline, how fast is the box moving as it arrives at the incline’s base?
4. A 24 kg block is moving across a horizontal floor at 8 m/s, when it strikes a horizontally-oriented
spring. If the spring compresses a distance of 9.3 cm in bringing the block to a stop, what is the
spring constant of this spring? (Consider friction to be negligible in this problem.)
5. A toy car rolls along the ground and approaches the base of a 12 o incline. The car rolls 40 cm
along the incline before it stops, because of gravity and friction acting on the car. If the
effective coefficient of friction between the car and incline is 0.38, calculate the speed the car
was rolling at, just as it started its way up the incline.
6. A certain object is moving at 7 m/s to the right when a 300 N force to the left begins acting on
it. The force acts for 3 seconds, and the object is moving at 9 m/s to the left when the force
stops acting. What is the mass of the object? (Use ideas from this unit.)
7. An ice-skating physicist with a mass of 80 kg performs an experiment where he is coasting
forward at 6 m/s while holding a 10 kg brick. He then throws the brick backward at 3 m/s
(relative to the ground). How fast is the physicist moving after he throws the brick?
8. A 2g marble moving to the right collides ellastically with a larger 3g marble moving to the left.
After the collision, the 2g marble is moving back to the left at 8.2 m/s, and the 3g marble is
moving to the right at 5.1 m/s. Calculate the velocity of each marble prior to the collision.
9.
A 6 kg bowling ball is given a push downward from the top of an incline, giving it an initial speed
of 3 m/s at a height of 50 cm above the bottom of the incline. Once it reaches the bottom, it
collides with another bowling ball, that has a mass of 7.3 kg and is at rest. After the collision,
the 7.3 kg ball moves forward at 1.4 m/s and the 6 kg ball rebounds back to roll back up the
incline. Assuming friction is negligible, what is the highest point the 6 kg ball reaches when it
rolls back up the incline?