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?

W= fd
where f is an applied force and d is the distance over which it is applied. when a parachuting skydiver is at constant velocity, he is experiencing "terminal velocity", the point at which his acceleration down is canceled out by air resistance. that means that the resisting force of the air is equal to his weight, but in the opposite direction. with this, we can solve for the work done by the force.
w = fd
w = (92.0)(9.81 m/s^2) (325)
w= 2.93 x 10^5 j
the value for work in this case is positive because it is pushing up on the skydiver, who has a downward force of gravity.
therefore the answer is 2.93 x 10^5 j