Physics
Momentum and Collisions
1. A 1200kg car is traveling at 25m/s. The driver brakes and the car stops in 5s. What force was applied by the brakes?
6000N
2. A 1500kg car is traveling 50m/s. The brakes can apply a force of 1000N. How long will it take the car to stop?
75s
3. How far will the car in problem 2 travel after the brakes are applied?
1875m
4. Two students of different masses sit on kinesthetic carts. They push off from one another. Shortly after the push, both of their velocities are measured at the same time. One cart plus student has a mass of 60kg and a velocity after the push of 1.2m/s. The other cart has a velocity of 0.8m/s. Determine the mass of the other student-cart. 90kg
5. A 25.0g bullet is fired at 400m/s into a 5 kg wooden block hanging from a string, as in the picture below. The block is at rest before the bullet hits it. The bullet becomes embedded in the wooden block.
a) What is the speed of the combined bullet + block? Show your work.
1.99m/s
b) How high will the block + bullet rise? Show your work.
.20m
c) Calculate the total kinetic energy before the collision and the total kinetic energy after the collision. Is it the same?
Before: 2000J After: 9.9J
6. Suppose a 0.200kg Gumby slides on ice at a speed of 0.750m/s, running into 0.350kg Pokey, who was initially motionless. Both being made out of clay, they naturally stick together. What is their final velocity?
.27m/s
7. The moon’s craters are remnants of meteor collisions occurring over the last 3 or 4 billion years and continuing today. Suppose a fairly large asteroid having a mass of 5.00X1012kg (about a kilometer across) strikes the moon at a speed of 15.0km/s.
a) At what speed does the 7.36X1022kg moon recoil after the perfectly inelastic collision?
.000000001km/s
b) How much kinetic energy is lost in the collision? Show your work.
5.625X1020
8. A 0.300kg ball, moving with a speed of 2.50m/s, has a head-on collision with a 0.600kg ball initially moving away from it at a speed of 1.00m/s. Assuming a perfectly elastic collision, what is the speed and direction of each ball after the collision? Show your work. Assume perfectly inelastic .167m/s
9. A 5kg ball is involved in the following situations:
A. It is traveling 10m/s and is smashes through a window. It slows down to 9m/s and continues on. The collision takes .025 seconds. Find the force on the ball. 200N
B. It is traveling 10m/s and it hits a soft wall and it slows down to 0. The collision takes .025 seconds. Find the force on the ball. 2000N
C. it is traveling 10m/s and it hits a wall. It bounces back from the wall at 8m/s in the opposite direction. The collision takes .025 seconds. Find the force on the ball. 3600N
D. The ball is traveling 10m/s and it hits another identical ball. The second ball moves forward at 3m/s. Find the velocity of the first ball and the kinetic energy lost in the collision. 7m/s
10. A 5kg rifle fires a .002kg bullet at 750m/s. Find the recoil speed of the rifle.
.3m/s
11. If the collision between the rifle in 10 and the marksman’s shoulder takes .05 seconds find the force on the shoulder.
1.5N
12. A pad is added to the rifle in 11. Find the force if the pad increased the time to .15s.
.5N
13. A tennis ball is thrown at a basketball. The tennis ball has initial velocity of 30m/s and after the collision the tennis ball is moving backwards at 25m/s. Find the velocity of the basketball.
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14. Write a problem you think could appear on multiple choice for the next exam. Write four answer choices with one right and the other three wrong but plausible to students who make common mistakes. Be ready to explain the problem, the solution and why you made the three wrong answer choices you did.
15. Write a problem you think could appear on free response for the exam. Make it have at least parts A-C. Be ready to explain the problem and the solution to the class in your group.