In one striking scene, a large truck coming down the street from the right colli

Question

In one striking scene, a large truck coming down the street from the right collides head-on with a small car that is travelling in the opposite direction. The two vehicles remain stuck together after the collision and move off in the original direction of the truck’s motion. You are amazed at the damage caused during the collision. As a physics student, you understand that the kinetic energy lost during the collision is the energy that was responsible for all the damage, so you decide to calculate it. By carefully rewinding and replaying the movie, you are able to determine that the car was originally moving at about 6 m/s and the truck at 4 m/s. After the collision, the two vehicles move together at 2 m/s. The car is a standard model and you estimate its mass to be 1000 kg.

Explanation / Answer

Truck’s mass is not given hence assume m2= 10500kg

Mass of car= m1=1000kg

KEi = 1/2m1v1i^2 + 1/2m2v2i^2 = 1/2*1000*6^2 + 1/2*10500*4^2 = 1.02*10^5 J

KEf = 1/2m1v1f^2 + 1/2m2v2f^2 = 1/2*1000*2^2 + 1/2*10500*2^2 = 2.3*10^4 J

Energy lost = KEf - KEi = 1.02*10^5 J - 2.3*10^4 J   = 7.9*10^4 J

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