Question

A 1000 kg Toyota, initially traveling at 40 mph, collides into the rear end of a 2000 kg Cadillac, initially stopped at a red light. The bumpers lock and the two cars skid for 2 seconds before coming to rest. Calculate the coefficient of kinetic friction between the tires and the road that is needed to bring the two cars to rest in 2 seconds.

Answer 1

find the velocity after collision
1000*v=(1000+2000)V
v= convert 40mph to m/s
solve for V.
KE after collision= 1/2 (1000+2000)V^2
friction work: mu*(totalmass)g*distance

but distance=avg velocity*time
= 1/2 V*t, t=2
solve for mu.