Momentum Momentum 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 )

Question Why do we need to wear seat belts?

Example ONE A 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 momentum b)Calculate the ball’s final momentum c)Calculate the ball’s change in momentum

Example TWO A 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.

Question Do you think the man survived the fall?

Impulse = “ change in momentum” Δp = p f – p i = mv f – mv i = m (v f – v i ) = m Δv = m a Δt = F Δt F = ma a = ΔvΔv ΔtΔt

Impulse = “ change in momentum” Δp = F Δt “Change in momentum is a result of force”

Question Do you think the man survived the fall?

Question How do air bags work?

Example THREE A 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