1.21

1.21

Tuesday, July 06, 2010

3:04 PM
· 1.21 use the ideas of momentum to explain safety features
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Example

Explain how motorcycle and bicycle helmets can protect their users during a collision

Answer
· Helmet or bare head, the change in momentum of your head during a collision is equal
· With a helmet, this change in momentum takes place over a longer time
· This means that the force needed to change the momentum of your head is less

or use the equation
· Impulse = Δp = F x t where Δp = constant
· cushioning in helmet => increases t
· and therefore decreases F

1.21 Plenary answers

13 March 2012

15:20

Physics for You p.147 Q2c

2c. Why is the front of a car designed to collapse in a serious collision? (3 marks)

· There is a force when you crash that decelerates the car (decreases your momentum)
· If the front of the car collapses (this is the crumple zone), this force acts for a longer time than if the front of the car were rigid
· This means that the force needed to change the car's momentum is less and there's less risk of injury to the driver

or use the equation
· Impulse = Δp = F x t where Δp = constant
· crumple zone increases t
· and therefore decreases F