The other day, I was arguing that a car traveling 70mph rear-ending a car traveling 55mph is the same as a car traveling 15mph rear-ending a stationary car. My argument was that, from the frame of reference of the car that was traveling 55mph, the energy of the other car is k(15(adsbygoogle = window.adsbygoogle || []).push({}); ^{2}), where k = mass/2. But then I thought, from the speedy car's frame of reference, the energy that must be dissipated to slow down to 55mph is k(70^{2}-55^{2}), which is not equal to k(15^{2}).

How come the energy that must be dissipated in the speedy car's frame of reference is different from the energy of the speedy car from the slower car's frame of reference?

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# Energy discrepencies depending on frame of reference

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