8.3 Conservation of Momentum

Which of the following is an example of an open system?

1. Two air cars colliding on a track elastically.
2. Two air cars colliding on a track and sticking together.
3. A bullet being fired into a hanging wooden block and becoming embedded in the block, with the system then acting as a ballistic pendulum.
4. A bullet being fired into a hillside and becoming buried in the earth.

A student sets up an experiment to measure the momentum of a system of two air cars, A and B, of equal mass, moving on a linear, frictionless track. Before the collision, car A has a certain speed, and car B is at rest. Which of the following will be true about the total momentum of the two cars?

1. It will be greater before the collision.
2. It will be equal before and after the collision.
3. It will be…

Cart A is moving with an initial velocity +v (in the positive direction) toward cart B, initially at rest. Both carts have equal mass and are on a frictionless surface. Which of the following statements correctly characterizes the velocity of the center of mass of the system before and after the collision?

1. $\frac{+ v}{2}$ before, $\frac{- v}{2}$ after
2. $\frac{+ v}{2}$ before, 0 after
3. $\frac{+ v}{2}$ before, $\frac{+ v}{2}$ after
4. 0 before, 0 after

Train cars are coupled together by being bumped into one another. Suppose two loaded train cars are moving toward one another, the first having a mass of 150,000 kg and a velocity of 0.300 m/s, and the second having a mass of 110,000 kg and a velocity of $- 0 . \text{120 m}/\text{s}$. (The minus indicates direction of motion.) What is their final velocity?

Consider the following question: A car moving at 10 m/s crashes into a tree and stops in 0.26 s. Calculate the force the seatbelt exerts on a passenger in the car to bring him to a halt. The mass of the passenger is 70 kg. Would the answer to this question be different if the car with the 70-kg passenger had collided with a car that has a mass equal to and is traveling in the opposite direction a…

A 1.80-kg falcon catches a 0.650-kg dove from behind in midair. What is their velocity after impact if the falcon’s velocity is initially 28.0 m/s and the dove’s velocity is 7.00 m/s in the same direction?