Work Done Kinetic Energy Momentum Vehicle Safety Features Energy and Momentum Work Done Kinetic Energy Momentum Vehicle Safety Features

Work Work done is the transfer of energy Work done (J) = Force (N) x distance (m)

Work done against gravity Work done against gravity = Gravitational Potential Energy (GPE) Flying saucer Work done (J) = Force (N) x distance (m) So Upwards: GPE (J) = Weight (N) x height (m) (weight = mass x gravity)

Work done against friction Rub hands together Brakes in a car

40 mph She has been hit initially on the pelvis. Her pelvis has broken. She has been thrown approximately 28m from the car, and has fallen to the ground onto her arm initially, with her head hitting the road next, causing her skull to be fractured (hence the trickle of blood from the ear, and the blood in the hair). She has grazes on the side of her face (on her cheeks and temple) from where she has slid along the road.

30 mph She has been hit initially on the pelvis. Her pelvis is bruised. Having been hit initially in the pelvis she is thrown approximately 16 metres and falls onto her side, fracturing her arm (though it would not look distorted). She then hits her head, but not so hard as to concuss her.

momentum (kg m/s)= mass(kg) x velocity(m/s) Air track

Conservation of momentum In some crashes momentum is conserved Eg, snooker balls colliding So total momentum before = total momentum after Massb4 x velocityb4 = massafter x velocityafter

Vehicle safety features and momentum Egg and sheet

force = change in momentum / time taken for the change How crumple zones work force = change in momentum / time taken for the change Stays constant Can change