1. The problem statement, all variables and given/known data A 0.75-kg block slides on a rough horizontal table top. Just before it hits a horizontal ideal spring its speed is 3.5m/s. It compresses the spring 5.7 cm before coming to rest. If the spring constant is 1200N/m, the internal energy of the block and the table top must have: A. not changed B. decreased by 1.9J C. decreased by 2.6J D. increased by 1.9J E. increased by 2.6J 2. Relevant equations delta E = delta Emec + delta Etherm + delta Eint = 0 3. The attempt at a solution basically I just did conservation of energy which I get that the change in mechanical energy is 1/2kx^2 - 1/2mv^2 = -2.6 J. Which means that the change in internal energy should be positive 2.6 J. Why does the answer key say that it's C?