You have been hired as an expert witness in a court case involving an automobile

Question

You have been hired as an expert witness in a court case involving an automobile accident. The accident involved a car of mass 1910 kg (car A) which approached a stationary car of mass 1080 kg (car B). The driver of car A applied his brakes 11 m before he crashed into car B. After the collision, car A slid 16 m while car B slid 30 m. The coefficient of kinetic friction between the locked wheels and the road was measured to be 0.80. Reconstruct the accident by calculating all the relevant velocities.

The speed of car A just before the breaks were applied.
km/h
The speed of car A just before the collision.
km/h
The speed of car A just after the collision.
km/h
The speed of car B just after the collision.
km/h

Explanation / Answer

Regardation=ug=0.8*9.8=7.84 m/s^2

After collision

Speed of A=sqrt(2*7.84*16)=15.83 m/s

Speed of B=sqrt(2*7.84*30)=21.7 m/s

Before collision ,let speed of A is v

Conserving momentum

1910*v=(1910*15.83)+(1080*21.7)

We got

v=28.03 m/s

Let initial speed of A is V

V=sqrt(28.03^2 +(2*7.84*11))

V=31.01 m/s

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