An 80 kg hockey player is skating at 5 m/s. he collides with the wall and comes to a stop in .2 s. what was the force of his impact on the wall

F = mass * acceleration
The 80kg hockey player was travelling at 5 m/s when he hit the wall.He stopped in .2 s, which means that he decelerated by 5m/s in .2 seconds.

This means this deceleration was 5 m / 0.2 s² = 25 m/s²

To calculate Force, multiply mass times acceleration
80kg times 25m/s² = 2,000 N

In this question, a hockey player with mass 80kg is skating with velocity 5m/s and then collide with a wall for 0.2 seconds. Force formula is mass multiplied by acceleration.
In this case, the velocity is changed into 5m/s into 0m/s in 0.2 second. Then the acceleration is: (5m/s - 0m/s) / 0.2 second= 25m/s^2

Then, the force on his impact should be: 

force= mass*acceleration
force= 80kg * 25 m/s^2= 2000N