5.7 Momentum

Question 1

state the equation used to calculate an object’s momentum.

Answer 1

momentum = mass x velocity

Question 2

what is the unit used for momentum?

Answer 2

kg m/s
kilogram metres per seconds

Question 2

in a closed system, what can be said about the momentum before and after a collision?

Answer 2

the total momentum before is equal to the total momentim afterwards.

Question 3

state an equation linking change in momentum, force and time.

Answer 3

force x time = change in momentum
F Δt = mΔv

Question 3

what quantity is equal to the force experienced in a collision?

Answer 3

the rate of change of momentum.

Question 4

if an object’s change of momentum is fixed, what is the only way to reduce the force that the object experiences?

Answer 4

increases the length of time over which the change of momentum occurs.

Question 4

explain how a seatbelt improves a passenger’s safety during a collision.

Answer 4

• passenger must decelerate from the vehicle’s velocity at impact to zero, meaning they undergo a fixed change of momentum
• the force they experience is equal to the rate of change of momentum
• seatbelts increase the time over which the force is applied, reducing the rate of change of momentum and therefore reducing the force experienced