Question

Displacement is vector quantity but why work done is scalar quantity? (W=F X Displacement)

Answer 1

It's defined as a dot-product (or scalar product) of force and displacement, both of which are vectors. A scalar product of two vectors gives a scalar result (aptly named!). dW=F⃗ ⋅S⃗ =∥F∥∥S∥cosθ dW=F→⋅S→=‖F‖‖S‖cos⁡θ (θθ being the angle between the vectors). No direction, only magnitude.