A car having a total mass of 2250 kg and traveling at 72.0 km/h smashes into a tree. The car is stopped in 0.250 s. The average force acting on the car during the collision is A. 1.80, 105 N.
B. 80.0 N.
C. 1.80 102 N
D. zero. E. 2.20 104

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.