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A 10 kg block moving at 10 m/s and a 20 kg block moving at 20 m/s travel toward each other along the same line and collide. If the collision is perfectly inelastic, how much thermal energy is generated?

1. 2500 J
2. 3000 J
3. 4000 J
4. 4500 J

Correct answer: 3000 J

Solution

Common velocity = (10*10 - 20*20)/30 = -10 m/s; initial KE = 4500 J, final KE = (1/2)(30)(10²) = 1500 J, so heat lost = 4500 - 1500 = 3000 J.

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