Starting from rest, a 4.0-kg body reaches a speed of 8.0 m/a in 20 s. What is te net force acting on the body?

The guy below is wrong!

F=ma

Where force = mass x acceleration

We dont have acceleration, a = change in velocity divided by the time taken.

a = v (final velocity) - u (initial) / t

a us 8-0 (at rest means u was 0) / 20 = 0.4

Using F=ma

F = mass x acceleration

F = 4 x 0.4

F=1.6 N