Starting from rest, a 4.0-kg body reaches a speed of 8.0 m/s in 2.0 s. what is the net force acting on the body?

The force that acted upon the body in for it to begin moving is represented by the equation:
F = ma
where F isis force, m is mass, and a is acceleration.

we know the mass is 4 kg.

we know the speed and the amount of time it took to get that speed. the amount of time it takes to reach a speed is acceleration. the equation for this is
a = (delta v) / t
a is acceleration. delta v is change in velocity. t is time.

So
a =(8 - 0 ) / 2
a = 4

F =4 * 4

F = 16 N