The 18-ft-long lightweight gate of Fig. P2.117 is a quarter circle and is hinged at H. Determine the horizontal force, P, required to hold the gate in place. Neglect friction at the hinge and the weight of the gate.

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.