MomentumMomentum is the amount of ‘oomph’ a moving object has.“The more ‘oomph’ the object has, the harder it is to stop”

p = mv (vector quantity)

p = momentum (measured in ________)m = mass (in kg)v = velocity (in ms-1)

QuestionWhy do we need to wear seat belts?

Example ONEA cricket ball of mass 500 g is bowled straight into the batter’s face at a speed of 35 ms-1. The batter blocks the ball with his bat, then the ball flies directly back towards the bowler’s face at 25 ms-1.a) Calculate the ball’s initial momentumb) Calculate the ball’s final momentumc) Calculate the ball’s change in

momentum

Example TWOA 120 kg man accidently falls off the roof of a building. The man’s velocity, the moment before he hits the ground, is 40 ms-1. He comes to a complete stop after he has hit the ground.Calculate his change in momentum.

QuestionDo you think the man survived the fall?

Impulse = “change in momentum”Δp = pf – pi

= mvf – mvi

= m (vf – vi) = m Δv = m a Δt = F Δt

F = ma

a = ΔvΔt

Impulse = “change in momentum”

Δp = F Δt“Change in momentum

is a result of force”

QuestionDo you think the man survived the fall?

QuestionHow do air bags work?

Example THREEA driver tries to slow down a runaway car by pushing against its motion. The car’s mass is 2100 kg and its initial velocity is 3.0 ms-1. Will the driver manage to stop the car if:• the resultant force on the car is 600 N

(against the car’s motion) and;• the force is applied for 9.0 seconds?

• Activity 10A (green book, pg. 123) Questions 1, 2, 3 and 6 only