http://www.ck12.org Chapter 7. Momentum Conservation
- You and your sister are riding skateboards (see Problem 3), but now she is riding behind you. You are holding
one end of a meter stick and she is holding the other. At an agreed time, you push back on the stick hard
enough to get her to stop. What happens to your speed? Choose one. (For the purposes of this problem
pretend you and your sister weigh the same amount.)
a. It stays the same.
b. It doubles.
c. It reduces by half. - You punch the wall with your fist. Clearly your fist has momentum before it hits the wall. It is equally clear
that after hitting the wall, your fist has no momentum. But momentum is always conserved! Explain. - An astronaut is using a drill to fix the gyroscopes on the Hubble telescope. Suddenly, she loses her footing
and floats away from the telescope. What should she do to save herself? - You look up one morning and see that a 30 kg chunk of asbestos from your ceiling is falling on you! Would
you be better off if the chunk hit you and stuck to your forehead, or if it hit you and bounced upward? Explain
your answer. - A 5.00 kg firecracker explodes into two parts: one part has a mass of 3.00 kg and moves at a velocity of
25 .0 m/s towards the west. The other part has a mass of 2.00 kg. What is the velocity of the second piece as
a result of the explosion? - A firecracker lying on the ground explodes, breaking into two pieces. One piece has twice the mass of the
other. What is the ratio of their speeds? - You throw your 6.0 kg skateboard down the street, giving it a speed of 4.0 m/s. Your friend, the Frog, jumps
on your skateboard from rest as it passes by. Frog has a mass of 60 kg.
a. What is the momentum of the skateboard before Frog jumps on it?
b. Find Frog’s speed after he jumps on the skateboard.
c. What impulse did Frog deliver to the skateboard?
d. If the impulse was delivered over 0.2 seconds, what was the average force imparted to the skateboard?
e. What was the average force imparted to the Frog? Explain. - Two blocks collide on a frictionless surface, as shown. Afterwards, they have a combined mass of 10 kg and
a speed of 2.5 m/s. Before the collision, one of the blocks was at rest. This block had a mass of 8.0 kg. What
was the mass and initial speed of the second block? - While driving in your pickup truck down Highway 280 between San Francisco and Palo Alto, an asteroid
lands in your truck bed! Despite its 220 kg mass, the asteroid does not destroy your 1200 kg truck. In fact,
it landed perfectly vertically. Before the asteroid hit, you were going 25 m/s. After it hit, how fast were you
going? - A baseball player faces a 80.0 m/s pitch. In a matter of.020 seconds he swings the bat, hitting a 50.0 m/s
line drive back at the pitcher. Calculate the force on the bat while in contact with the ball. - An astronaut is 100 m away from her spaceship doing repairs with a 10.0 kg wrench. The astronaut’s total
mass is 90.0 kg and the ship has a mass of 1. 00 × 104 kg. If she throws the wrench in the opposite direction of
the spaceship at 10.0 m/s how long would it take for her to reach the ship? - A place kicker applies an average force of 2400 N to a football of.040 kg. The force is applied at an angle of
20 .0 degrees from the horizontal. Contact time is .010 sec.
a. Find the velocity of the ball upon leaving the foot.
b. Assuming no air resistance find the time to reach the goal posts 40.0 m away.
c. The posts are 4.00 m high. Is the kick good? By how much?