To test the impact performance of a 10 cm thick gymnastics mat, a 20 kg cylindrical mass is dropped onto the mat from a height of 1 m above the mat. During the impact, the cylindar's vertical velocity reaches zero at the instant the mat has compressed to only 4 cm thick.
a. How much kinetic energy does the cylindar have at the instant just before it contacts the mat?
b. How much work does the mat do to stop the fall of the cylinder?
c. What average vertical force does the mat exert on the cylinder during the impact, from contact until the cylinder's vertical velocity is zero?