Two equations are used for this problem: Newton's 2nd law of motion, and also an equation derived from the 2nd law specialized for linear motion at constant acceleration.
(1) F = ma
(2) 2ax = v2^2 - v1^2
We will use equation 2 first:
2a(0.3025 m) = (3.2m/s)^2 - 0^2
a = 16.926 m/s^2
Using equation 1:
F = ma
125 N = m(16.926 m/s^2)
m = 7.39kg
