Chapter 5 - Newton's Laws of Motion - Problems and Conceptual Exercises - Page 140: 5

Average force = 1590 N

We know that $a=\frac{v_f-v_i}{\Delta t}$ $a=\frac{12m/s-0m/s}{4.0\times 10^{-3}s}$ $a=3\times 10^{3}m/s^2$ Now $F=ma$ We plug in the known values to obtain: $F=(0.53Kg)(3\times 10^3m/s^2)$ $F=1.59\times 10^3N$ $F=1590N$