Extra Credit Problems 3rd Nine Weeks
For extra credit for the 3rd nine weeks, you can choose up to 20 problems for a maximum of 20 pts. You can choose any
question you want, but you must show all your work. Use the appropriate significant figures in your answer. If a problem
you choose has a part a, b, c, etc., then each part counts as a separate problem. In other words, you don’t have to do part b
of a problem if you don’t want to. I won’t give you the answers, but if you are resourceful enough, you can find the answers
to at least some of the problems. The final date I will accept your work is Friday, March 8, 2013. The problems you can
select from are listed below: (As we cover new material, I may add additional problems for you to choose from)
Pg. 186 – 188
#33 - #41, #43, #44 - #48, and #50 – 52
Pg. 199
Practice A
Pg. 201
Practice B
Pg. 203
Practice C
Pg. 223
#11 - #14
Pg. 225
#35 - #36
Pg. 884 – 885
#139 - #143
#145 - #147
#149 - #155
Problem
1. A 37 kg child on roller skates, initially at rest, rolls 2.0 m down an incline at an angle of 17.0 with the
horizontal. If there is no friction between incline and skates, what is the kinetic energy of the child at the bottom
of the incline? (g = 9.81 m/s )
2. On a given occasion, Old Faithful geyser in Yellowstone National Park shoots water to a height of 47.1 m. With
what velocity does the water leave the ground during this eruption? (Assume no air resistance and that g = 9.81
m/s .)
3. A pole vaulter clears 6.41 m. With what velocity does the vaulter strike the mat in the landing area? (Assume no
air resistance and that g = 9.81 m/s .)
4. A bobsled zips down an ice track, starting from rest at the top of a hill with a vertical height of 170 m.
Disregarding friction, what is the velocity of the bobsled at the bottom of the hill? (g = 9.81 m/s )
5. A pendulum with a mass of 4.0 kg is released from a height of 2.9 cm above the height of its resting position.
How fast will the pendulum be moving when it passes through the lowest point of its swing?
6. What is the average power output of a weightlifter who can lift 260 kg to a height of 1.9 m in 1.8 s?
7. A jet engine develops 1.1 10 N of thrust to move an airplane forward at a speed of 9.3  10 km/h. What is
the power output of the engine?
8. A 1.71  10 kg sports car accelerates from rest to 25.8 m/s in 7.41 s. What is the average power output of the
automobile engine?
9. Water flows over a section of Niagara Falls at a rate of 1.30  10 kg/s and falls 49.5 m. What is the power of
the waterfall?
10. Compare the momentum of a 5450 kg truck moving at 8.00 m/s to the momentum of a 2725 kg car moving at
16.0 m/s.
11. Which has a greater momentum—a truck with a mass of 3530 kg moving at a speed of 21 m/s or a car with a
mass of 1620 kg moving at a speed of 54 m/s?
12. What velocity must an 1120 kg car have in order to have the same momentum as a 3360 kg truck traveling at a
velocity of 16 m/s to the west?
13. A 5.68  10 kg tennis ball moves at a speed of 13 m/s. The ball is struck by a racket, causing it to rebound in
the opposite direction at a speed of 18 m/s. What is the change in the ball’s momentum?
14. A rubber ball with a mass of 0.41 kg is dropped onto a moveable steel plate. The ball’s speed just before impact
is 2.1 m/s and just after impact is 1.9 m/s. What is the change in the ball’s momentum?
15. A cricket ball with a mass of 0.158 kg moves at a speed of 17 m/s. Then the ball is hit by a bat and rebounds in
the opposite direction at a speed of 18 m/s. What is the change in momentum of the ball?
16. A ball with a mass of 0.70 kg and a speed of 7.0 m/s strikes the side of a large box and bounces straight back
with a speed of 4.0 m/s. What is the change in momentum of the ball?
17. A baseball bat strikes a baseball with a force of 37 N. The bat is in contact with the ball for 0.19 s. What is the
magnitude of the change in momentum of the ball?
18. A pool cue strikes a 0.16 kg billiard ball with a force of 11 N. The cue remains in contact with the ball for 0.065
s. The ball was initially at rest. What is the final speed of the ball?
19. A player at first base catches a throw traveling 38 m/s. The baseball, which has a mass of 0.145 kg, comes to a
complete stop in the glove after 0.14 s. Assuming the force of the glove was uniform, what force did the glove
exert on the ball?
20. A 46 kg trapeze artist falls straight down onto a safety net. The trapeze artist’s initial speed as she hits the net is
9.8 m/s, and the net stretches 1.1 m vertically as she comes to a stop. What average net force does the trapeze
artist experience while the net breaks her fall? How many “g’s” of acceleration does she experience on average?
(1 g = 9.81 m/s )
21. A 56.0 kg diver jumps off a diving platform, rises about 1.0 m above the platform, then falls to the pool. What is
the diver’s momentum at her highest point in the dive?
22. Use the impulse-momentum theorem to find the diver’s momentum after falling for 1.29 s.
23. The diver strikes the water at a speed of 13.9 m/s, and then slows to a stop underwater in 0.65 s. What force does
the water exert on the diver?
24. A train with a mass of 2.1 10 kg is moving at 12 m/s when the engineer applies the brakes. If the braking
force is constant at 3.7 10 N, how long does it take the train to stop? How far does the train travel during this
time?