Changes in Momentum

Question 1

What happens to a moving object’s momentum when a non-zero resultant force acts on that object?

Answer 1

The force causes a change in the object’s momentum

Question 2

Two flying ducks collide in mid-air and bounce off each other in different directions. What do you know about the two forces that caused the changes in the velocities of the ducks? Which of Newtons’ Laws is this an example of?

Answer 2

They are equal. This is an example of Newton’s Third Law

Question 3

The force needed to accelerate a car to 30 m/s in 5 seconds is 6000 N. What is the force required for the car to accelerate to 30 m/s in half of this time?

Answer 3

12000N
F = (mv-mu) / t. If the time is halved but the mass and velocities are the same, the force has to double. 2 x 6000 = 12000N

Question 4

A force acts on a 10 kg beanbag for 2 seconds. It causes the beanbag’s velocity to increase by 4 m/s. Use F = (mv-mu)/t to find the magnitude of the force

Answer 4

20N

F = (mv-mu) / t = (m(v-u)) / t, so the magnitude of the force acting on the beanbag is (10 x 4) / 2 = 20N

Question 5

A freestyle skier practises new tricks into a large pit filled with foam. Explain why it is safer for the skier to land in a foam pit rather than on solid ground.

Answer 5

Foam is compressible so it will increase the time it takes the skier to come to a stop. This means the change of momentum will happen more slowly, so the force on the skier will be greatly reduced. The reduced force on the skier is less likely to cause injury