mastering physics To understand how to compute the work done by a constant force acting on a particle that moves in a straight line. In this problem, you will calculate the work done by a constant force. A force is considered constant if F⃗ (r⃗ ) is independent of r⃗ . This is the most frequently encountered situation in elementary Newtonian mechanics.

Complete Question

The complete question is shown of the first uploaded image

Explanation:

 The  force vector acting upon the particle is (The magnitude is F )

  The displacement vector from point B to A is   (The magnitude is  L )

Generally workdone is mathematically represented as

But from the question we are to that vector L has a magnitude L  and  makes and angle with the positive x-axis

also  we are told that Force is pointing to the left and is parallel to the horizontal  axis (i.e at angle   (180°))

Generally the angle between the is  

Hence the workdone is mathematically represented as

=>    

Here the negative sign shows that the displacement is acting in opposite direction to the direction of the workdone (the force applied )