We have the formula for Force: F = ma, which m is mass and a is the acceleration. We are given the mass, so we now compute for the acceleration: a = (V^2 - Vo^2) / 2(X), where a is the acceleration, V is the final velocity, Vo is the initial velocity and X is the distance. We assume the man started from rest, we have: a = [(40 m/s)^2 - (0 m/s)^2] / 2(20 m) = 40 m/s^2. Now we find the force: F = (70 kg)(40 m/s^2) = 2800 N.
