Force and rate of change of momentum (safety design)

Question 1

Why do cricket or baseball fielders pull their hands back as they catch a fast ball?

• A. It changes the ball's momentum to zero instantly
• B. It increases the ball's speed
• C. It makes the ball lighter
• D. It increases the time to stop the ball, reducing the force on their hands

Question 2

A 80 kg passenger moving at 12 m/s is brought to rest in 0.5 s by a seat belt and airbag. What is the average force on the passenger, in N?

Answer N

Question 3

A helmet increases the time for a head to stop in a fall from 0.01 s to 0.04 s. The change in momentum is the same. By what factor is the average force reduced?

Answer 

Question 4

How do crumple zones in a car reduce injuries?

• A. They stop the car instantly
• B. They reduce the change in momentum to zero
• C. They increase the time taken to stop, so the force on passengers is smaller
• D. They make the car heavier

Question 5

A 70 kg passenger moving at 20 m/s is brought to rest in 0.2 s by a seat belt and airbag. What is the average force on the passenger, in N?

Answer N

Question 6

A helmet increases the time for a head to stop in a fall from 0.02 s to 0.08 s. The change in momentum is the same. By what factor is the average force reduced?

Answer 

Question 7

Why do gymnasts land on thick soft mats?

• A. Mats bounce them higher
• B. The mat reduces their mass
• C. The mat increases their speed
• D. The mat increases stopping time, reducing the force on their legs

Question 8

A 60 kg passenger moving at 15 m/s is brought to rest in 0.5 s by a seat belt and airbag. What is the average force on the passenger, in N?

Answer N

Question 9

A helmet increases the time for a head to stop in a fall from 0.01 s to 0.05 s. The change in momentum is the same. By what factor is the average force reduced?

Answer 

Question 10

How do crumple zones in a car reduce injuries?

• A. They increase the time taken to stop, so the force on passengers is smaller
• B. They make the car heavier
• C. They reduce the change in momentum to zero
• D. They stop the car instantly

Question 11

A 70 kg passenger moving at 15 m/s is brought to rest in 0.5 s by a seat belt and airbag. What is the average force on the passenger, in N?

Answer N

Question 12

A helmet increases the time for a head to stop in a fall from 0.02 s to 0.1 s. The change in momentum is the same. By what factor is the average force reduced?

Answer 

Question 13

Why do cyclists' helmets contain crushable foam?

• A. Foam makes the helmet bounce
• B. Foam reduces air resistance
• C. Foam is heavier than plastic
• D. Crushing foam increases the time the head takes to stop

Question 14

A 70 kg passenger moving at 12 m/s is brought to rest in 0.2 s by a seat belt and airbag. What is the average force on the passenger, in N?

Answer N

Question 15

A helmet increases the time for a head to stop in a fall from 0.05 s to 0.2 s. The change in momentum is the same. By what factor is the average force reduced?

Answer 

Question 16

How do crumple zones in a car reduce injuries?

• A. They make the car heavier
• B. They stop the car instantly
• C. They increase the time taken to stop, so the force on passengers is smaller
• D. They reduce the change in momentum to zero