Question

When jumping straight down, you can be seriously injured if you land stiff-legged. One way to avoid injury is to bend your knees upon landing to reduce the force of the impact. A 78.1 kg man just before contact with the ground has a speed of 6.58 m/s. In a stiff-legged landing he comes to a halt in 2.05 ms. Calculate the average net force that acts on him during this time.

Answer 1

Average net force is equal to rate of change of momentum.

              F = m ( v - u ) / t

Here, m is mass, v is final velocity , u is initial velcotiy, and t is time

             F = ( 78.1 kg) (6.58 m/s - 0) / (2.05x10^-3 s )

                  = 250681 N