A police officer is investigating a crash between two identical cars of mass m =

Question

A police officer is investigating a crash between two identical cars of mass m = 1500 kg. After the
crash, the cars have stuck together and left skid marks for a distance of d = 10 m before coming
to a stop. The officer determines that the coeffient of kinetic friction between the cars and road
is ?k = 0.8. When interviewing the drivers, the officer finds out that one car was stationary and
the other was moving before the collision. The officer gives the driver of the moving car a speeding
ticket. What is the speed that the officer writes on the ticket?

Explanation / Answer

a = u.g = 0. 8x 9.8 = 7.84 m/s2

using v^2 - u ^2 =2ad

0 - u^2 = 2 x -7.84 x 10

u =12.52 m/s

uysing momentum conservation,

1500v + 1500 x 0 = (1500 +150) x 12.52

v = 25.04 m/s

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