6. Collisions and momentum

Question 1

The linear motion of an object is directly proportional to what?

Answer 1

The object’s mass and velocity.

Question 2

What is impulse?

Answer 2

The force on an object over a period of time.

Question 3

Impulse is directly proportional to what?

Answer 3

Force and time.

Question 4

Conservation of momentum states what?

Answer 4

The initial momentum in a closed system equals the final momentum of the closed system.

Question 5

What are the 3 types of collision?

Answer 5

Explosions, objects that stick together, objects that remain separate.

Question 6

What is an elastic collision?

Answer 6

A collision where the kinetic energy of the system before the collision is equal to the kinetic energy of the system after the collision.

Question 7

What is an inelastic collision?

Answer 7

Collisions in which the kinetic energy of the system before the collision does not equal the kinetic energy after the collision.

Question 8

What is the centre of mass?

Answer 8

The average position of all parts of the system.

Question 9

What is significant about the centre of mass?

Answer 9

It is the point around which the system freely rotates.

Question 10

Ball A is a 1.50 kg ball moving at 8.00 m/s south. It strikes Ball B, a 2.00 kg ball moving at 3.00 m/s south. The velocity of Ball B after the collision is 4.50 m/s south. What is the momentum of Ball B after the collision?

Answer 10

9

Question 11

Ball A is a 1.50 kg ball moving at 8.00 m/s south. It strikes Ball B, a 2.00 kg ball moving at 3.00 m/s south. The velocity of Ball B after the collision is 4.50 m/s south.

Answer 11

12 before the collision, 9 after the collision

Question 12

A truck on a freeway is going 50 m/s. If it has a momentum of 100 kg*m/s, what is the mass of the truck?

Answer 12

2 kg

Question 13

The sum of all the external forces on a system of particles is zero. Which of the following must be true of the system?

• The total mechanical energy is constant.
• The total potential energy is constant.
• The total kinetic energy is constant.
• The total linear momentum is constant.
• It is in static equilibrium.

Answer 13

The total linear momentum is constant.

Question 14

In the collision pictured below, the black box (62kg), moves at a velocity of 13m/s and hits the grey box (62kg).

1. What is the momentum of the black box when it collides with the grey box?
2. What is the velocity and momentum of the grey box after the collision?
3. What kind of collision is this depicting?

Answer 14

1. 806N
2. Since both masses are equal, the velocity of the grey box after the elastic collision is the same as the black box’s velocity before the collision, 13m/s. Because of the Law of Conservation of Momentum, the momentum transfers from the black box to the grey box equaling 806N.
3. This is a picture of an elastic collision with equal masses.

Question 15

In the perfectly elastic collision pictured below, the black sphere (23kg), moves at an initial velocity of 17m/s, and the grey sphere (41kg), moves at initial velocity of -7m/s.

1. What is the velocity of the black sphere as it moves away from the grey sphere?
2. What is the velocity of the grey sphere as it moves away from the black sphere?
3. What is the momentum of each sphere before impact?

Answer 15

1. What is the velocity of the black sphere as it moves away from the grey sphere? -4.8 m/s
2. What is the velocity of the grey sphere as it moves away from the black sphere? 12.22 m/s
3. What is the momentum of each sphere before impact? 287N