Question

if displacemt of a body is 0 then force will be 0 but why still have pain if the force is zero

Answer 1

This is because pain or tiredness is not considered in the formula W = F × s

Answer 2

We can also take an example
If we push a wall it doesn’t move so we are not able to move the wall .
The displacement is 0 so the force will also be 0.