5.1.4 Solving Problems Using Conservation of Momentum

Question 1

Solving Problems Using Conservation of Momentum

Answer 1

• Use conservation of momentum ( or ) when
• Conservation of momentum is useful for understanding collisions where friction is not important.
• Explosions can be understood using conservation of momentum.

Question 2

A firecracker is lit at rest and eventually explodes into three pieces. The three pieces fly off horizontally. Using the values given in the diagram, which of the following is the velocity of the smallest piece?

Answer 2

−20 cm / s

Question 3

True or false?
If two identical cars moving the same speed crash into each other head-on, more damage is done to the occupants of the cars if the two cars bounce off each other than if the two cars stick together.

Answer 3

true

Question 4

Two carts on an airtrack (i.e., no friction), each with a mass of 3 kg, are moving to the right. Cart 1 has a speed of 0.5 m / s, and Cart 2 has a speed of 1.5 m / s and is following Cart 1. When the faster cart bumps into the slower cart, they stick together. How fast do the two carts move after this collision?

Answer 4

1.0 m / s

Question 5

When a stationary uranium nucleus undergoes fission, it breaks into two unequal chunks that fly apart. Which of the following is true of both the speeds and momentum vectors of the chunks?

Answer 5

The chunks have different speeds and different momentum vectors.

Question 6

If an 18-wheeler and a compact sedan collide head-on, which vehicle experiences a greater change in momentum?

Answer 6

They experience the same change in momentum.

Question 7

A glass ball is thrown straight down on concrete and breaks into four pieces that move away from each other horizontally. Using the information given in the diagram, which of the following is the speed of the largest piece?

Answer 7

1.5 m / s

Question 8

A 4 kg object moving to the right with a speed of 2 m / s collides head-on with a 3 kg object moving to the left with a speed of 3 m / s. If, after the collision, the 3 kg object moves to the right with a speed of 3 m / s, what would be the direction and speed of the 4 kg object after the collision? Based on your result, is this collision physically possible?

Answer 8

Left at a speed of 2.5 m / s; not physically possible.

Question 9

A pendulum with a bob of mass m is pulled up an initial height hi  and let go so the bob swings. At the bottom of the bob’s swing, it collides and sticks to an equal mass that is at rest. What is the maximum height hf  the combined mass is able to swing up to?

Answer 9

hi/4

Question 10

A 2 kg object collides head-on with a 9 kg object moving 4 m / s to the right. The two objects stick together and the combined object is at rest. What is the velocity of the 2 kg object at the time of the collision?

Answer 10

−18 m / s