A 70 kg man just before contact with the ground has a speed of 5 m/s In a stiff-legged landing he comes to a halt in 7ms (miliseconds). Keeping in mind that the average net force acting on the man includes both the force of the ground on the man and the gravity force, find the force of the ground on the man.

To find the force of the ground on the man, we can use Newton's second law of motion, which states that the net force acting on an object is equal to its mass multiplied by its acceleration.

First, we need to calculate the acceleration experienced by the man during the landing. We can use the formula:

acceleration = (final velocity - initial velocity) / time

Here, the final velocity is 0 m/s since the man comes to a halt, the initial velocity is 5 m/s, and the time is 7 ms. We need to convert the time to seconds by dividing it by 1000:

acceleration = (0 m/s - 5 m/s) / (7 ms / 1000)
acceleration = -5 m/s / 0.007 s
acceleration ≈ -714 m/s^2

Since the man is coming to a halt, the acceleration is negative, indicating that it is in the opposite direction of the motion.

Now, we can calculate the force of the ground on the man using Newton's second law:

force = mass * acceleration

The mass of the man is given as 70 kg, and the acceleration we just calculated is -714 m/s^2:

force = 70 kg * -714 m/s^2
force ≈ -49980 N

The force of the ground on the man is approximately 49980 N. The negative sign indicates that the force is in the opposite direction to the motion of the man.