Momentum

Question 1

What is momentum

Answer 1

The product of mass and velocity of an object

Question 2

What is the equation for momentum

Answer 2

p = mv

Momentum (kgm/s) = Mass(kg) x Velocity (m/s)

Question 3

What is the conservation of linear momentum

Answer 3

Momentum is always conserved in any interaction (where no external forces act) this means the momentum before an event is equal to the momentum after

Question 4

Explain why momentum changes as an object strikes a wall without rebounding

Answer 4

• When an object strikes a wall it exerts a force on the wall
• And the wall excerpts a force on the object (This is Newton’s 3rd Law)
• The size of the force will be mv - mu / t (This is Newton’s 2nd Law)
• Since the object stops then the final velocity is 0 meaning the momentum becomes 0
• The momentum is transferred to the wall because momentum is always conserved

Question 5

Explain how to calculate the force of an object when it strikes a wall and rebounds

Answer 5

• The size of the force will be mv - mu / t (This is Newton’s 2nd Law)
• Since the object rebounds, the initial velocity will be positive and the final velocity will be negative (or vice versa)

Question 6

What is force in terms of momentum

Answer 6

F = (mv -mu) / ∆t

The rate of change of momentum

Question 7

Use Newton’s 2nd Law with the equation for momentum to find force as the rate of change of momentum

Answer 7

F = ma (Newton’s 2nd Law)
a = Δv / Δt (Suvat)

F = Δ(mv) / Δt

This shows that force is the rate of change of momentum

Question 8

What is FΔt

Answer 8

Impulse, and impulse is equal to Δ(mv)

Question 9

What is impulse

Answer 9

The change in momentum

Question 10

What are some designs made to transport in order to reduce momentum conservation issues

Answer 10

• Crumple zones in cars, seat belts and air bags all increase the impact time of the car or passenger
• This causes the forces exerted on passengers to decrease
• This means people are less likely to be seriously injured

Question 11

What are the two types of collisions

Answer 11

• Elastic - where both momentum and kinetic energy is conserved
• Inelastic - only momentum is conserved, the kinetic energy is converted into other forms (e.g. heat, sound) so may be larger or smaller

Question 12

Describe examples of inelastic collisions

Answer 12

• If the objects in a collision stick together after the collision (car crash)
• An explosion (the kinetic energy is greater than before the collision)