A 1.81-kg juggling ball is thrown with a kinetic energy of 4.00 J. It then hits a wall and comes back a with half its original speed. The ball's kinetic energy after hitting the wall must be J. Round your answer to three significant figures.

A47.2 g block of copper whose temperature is 480 k is placed in an insulating box with a 91.8 g block of lead whose temperature is 200 k. (a) what is the equilibrium temperature of the two-block system? (b) what is the change in the internal energy of the two-block system between the initial state and the equilibrium state? (c) what is the change in the entropy of the two-block system? the heat capacities of copper and lead are 386 j/kg·k and 128 j/kg·k, respectively.