A 991kg car traveling initially with a speed of 32.2m/s in an easterly direction crashes into the rear end of an 8650kg truck moving in the same direction at 17.8m/s. The velocity of the car right after the collision is 10.4m/s to the east. How much mechanical energy is lost in the collision? Answer in J.(adsbygoogle = window.adsbygoogle || []).push({});

I already solved for the velocity of the truck after the collision: 20.298m/s.

I did Mech Energy = Initial kinetic energy - final kinetic energy

Initial

Ke= .5(991)(32.3)^2 + .5(8650)(17.8)^2 = 1887283.195J

Final

Ke= .5(991)(10.4)^2 + .5(8650)(20.298)^2 = 1835531.357J

The difference between the two is 51751.838J and it's incorrect. I've checked my math too many times and I still get the same answer. Or is the answer supposed to be -51751.838J? I figured that since they said "energy is lost," they only wanted the magnitude of energy lost. I'm stumped.

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# Homework Help: Mechanical energy lost

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