Question

A bullet of mass 20 g, travelling at a speed of 350 ms −1 , strikes a steel plate at an angleof 30º with the plane of the plate. It ricochets off at the same angle, at a speed of320 ms −1 . What is the magnitude of the impulse that the steel plate gives to theprojectile? If the collision with the plate takes place over a time ∆t = 10 −3 s, what is theaverage force exerted by the plate on the bullet?

Answer 1

let X axis be the axis perpendicular to the plate. Y axis be along the plate.

The momentum along Y axis remains the same.
Initial momentum along x axis = - m u sin 30 = - m u / 2
final momentum along x axis = + m v sin 30 = m v /2

change of momentum = impulse
    = m (v+u)/2 = 0.020 * (350+320)/2 kg-m/s
            = 6.70 kg-m/s
force = 6.70/0.001 sec    = 6,700 N