Acircus performer is putting together an act that involves lying on a bed of nails without getting hurt. the tip of each nail has a radius of 1 mm and the performer has a mass of 65 kg. a typical human pain threshold for pressure on the skin is about 0.40.4mpa (1\text{mpa} = 10^61mpa=10 6 pa). this is the minimum pressure that causes a sensation of pain. if the performer stepped on a single nail, what pressure would the nail exert on his foot?

Aperson gives a shopping cart an initial push along a horizontal floor to get it moving, and then lets go. the cart travels forward along the floor, gradually slowing as it moves. consider the horizontal force(s) on the cart while it is moving forward and slowing. which of the following statements is correct? (a) both a forward and a backward force are acting on the cart, but the forward force is larger. (b) only a forward force is acting which diminishes with time. (c) both a forward and a backward force are acting on the cart, but the backward force is larger. (d) only a backward force is acting, no forward force.