Asked by Jojo

A 51.2-kg skater is standing at rest in front of a wall. By pushing against the wall she propels herself backward with a velocity of -1.99 m/s. Her hands are in contact with the wall for 1.20 s. Ignore friction and wind resistance. Find the average force she exerts on the wall (which has the same magnitude, but opposite direction, as the force that the wall applies to her). Note that this force has direction, which you should indicate with the sign of your answer.
Answered by R_scott
acceleration = (1.99 m/s) / 1.20 s

force = mass * acceleration ... one of Newton's laws

because her resultant velocity is negative
... the force she exerts on the wall is positive