Question

A bullet of mass 20 g, travelling at a speed of 350 ms−1

, strikes a steel plate at an angle

of 30º with the plane of the plate. It ricochets off at the same angle, at a speed of

320 ms−1

. What is the magnitude of the impulse that the steel plate gives to the

projectile? If the collision with the plate takes place over a time ∆t = 10−3 s, what is the

average force exerted by the plate on the bullet?

Answer 1

mass = 20 g = 0.2 kg
u = 350 m/s
v = 320 m/s

u = 350 cos30°
= 350×(√3/2)
= 175√3 m/s

v = -320 cos30°
= -320×(√3/2)
= -160√3 m/s

Time of collision = ∆t = (10-3)sec

Impulse
= (mv-mu)/∆t
= m(v-u)/∆t

= 0.2(-160√3-175√3) / (10-3)

= 0.2×(-15√3)/7
= -(3/7)√3
= 0.428√3 N.s
______________________
Hence the average force exerted by the steel plate on the bullet is 0.428 N