A child is riding in a child-restraint chair, securely fastened to the seat of a car. Assume the car has speed 47 km/h when it hits a tree and is brought to rest in 0.20 s. The mass of the child is 19 kg. Assuming constant deceleration during the collision, estimate the net horizontal force that the straps of the restraint chair exert on the child to hold her in the chair.

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.