C9 FORCE AND MOMENTUM

Question 1

State the formula for momentum, and its units. (1)

Answer 1

⇒ Momentum = Mass x Velocity

(ρ/kg ms⁻¹) (m/kg) (v/ms⁻¹)

Question 2

Define Newton’s second law in terms of momentum. (1)

Answer 2

⇒ A resultant force is proportional to the change in momentum per second.

Question 3

State Newton’s formula for the second law in terms of changing momentum (changing mass or velocity). (1)

Answer 3

⇒ F= Δ(mv)/Δt (1)
⇒ F = Resultant force / Newtons (N)
⇒ Δ(mv)/Δt = Rate of change of momentum / kg ms⁻²

Question 4

Define impulse, state its formula with units. (2)

Answer 4

Impulse: the product of force and time
Impulse = Change in momentum
(FΔt/Ns) = ( Δ(mv)/kg ms⁻¹)

Question 5

How would you work out the momentum of a force-time graph? (1)

Answer 5

⇒ The area under the graph represents the change of momentum or the impulse of the graph. (1)

Question 6

Give three safety measures of how cars slow down impact time. (3)

Answer 6

⇒ Crumple zones
⇒ Seat belts
⇒ Airbags

Question 7

what do crumple zones do? (4)

Answer 7

⇒ Crumple zones deform on impact (1)
⇒ Increases the time taken for the car to stop (1)
⇒ increasing the impact (1)
⇒ Decreasing the force on the passengers (1)

Question 8

What do seat belts do in terms of momentum? (3)

Answer 8

⇒ Seatbelts stretch (1)
⇒ Increasing time taken for the wearer to stop (1)
⇒ Reduces force on chest (1)

Question 9

What do airbags do in terms of momentum?

Answer 9

slows down the passenger more gradually (1)
increasing time taken for head to stop (1)
reduces impact force (1)
prevents head from hitting hard surfaces in the car (1)

Question 10

If given a force-time diagram with a curve, how would you calculate the momentum? (3)

Answer 10

⇒Calculate the momentum for a single block (1)
⇒ Count how many blocks there are under the curve (1)
⇒ Change in momentum = momentum of 1 block x sum of blocks (1)

Question 11

What does the principle of conservation of momentum state? (2)

Answer 11

⇒ For a system of interacting objects, the total momentum remains constant (1)
⇒ Provided no external resultant forces acting on the system (1)

Question 12

Define what an elastic collision is. (1)

Answer 12

⇒ An elastic collision is one where there is no loss of kinetic energy of momentum. (1)

Question 13

State what an inelastic collision is. (1)

Answer 13

An inelastic collision is one where kinetic energy isn’t conserved and the colliding objects have less kinetic energy after the collision than before the collision. (1)

Question 14

State the equation for kinetic energy.

Answer 14

Eₖ = (1/2)(m)(v)²
Eₖ: Joules
m: kg
v: ms⁻¹