Momentum: Answers

What is the momentum of a car travelling at a velocity of 12 m/s with a mass of 1500 kg?

Momentum = mass x velocity

Momentum = 1500 x 12 = 18,000 kg m/s

A 3000 kg car travelling at a speed of 20 m/s collides into a car which was travelling 10 m/s and has a mass of 2500 kg. What is their momentum after the collision?

The conservation of momentum states that the total momentum before a collision = total momentum after a collision.

• Momentum of car 1 = 3000 x 20 = 60 000 kg m/s

• Momentum of car 2 = 2500 x 10 = 25 000 kg m/s

• Total momentum before the collision = 60,000 + 25,000 = 85,000 kg m/s

• So the total momentum after the collision = 85,000 kg m/s

Cristiano Ronaldo kicks a 400 g football from rest which reaches a velocity of 50 m/s in 5 seconds. With what force did he kick the ball?

• Force = change momentum / time taken

• Momentum = mass x velocity

• Momentum = 0.4 kg x 50 = 20 kg m/s

• Force = 20 / 5 = 4 N

Explain how safety features work to reduce the force of impact during a car crash?

Car safety features work by increase the amount of time it takes for a vehicle to come to a stop during a crash. If the time is increased, force decreases since force = momentum / time.

State Newton’s third law of motion and give an example.

Newton’s third law states that when two objects interact, they exert equal and opposite forces on each other. An example could include sitting on a chair. There is a downwards force acting from the weight of the person to the chair but an equal and opposite force from the chair acting upwards.