Question

A force F of strength 20 N acts on an object of mass 3 kg as it moves a distance of 4 m. If F is perpendicular to the 4 m displacement, the work it does is equal to how many joules?

Answer 1

Data:
$F = 20 [N]$
$m = 3 [kg]$
$s = 4 [m]$
Work is calculated from the following formula:
$W = F \cdot s \cdot cos(a)$
Where a is the angle between force vector and displacement vector. When force is perpendicular to displacement, a = 90 deg and cosine of this angle = 0.
Therefore, the work this force does = 0 [J]

Answer 2

Work = (displacement) x (force in the direction of the displacement)

Since none of the force is in the direction of the displacement, the work it does
is zero. Something else is making the object move.  It's not the 20N force.