A body constrained to move along the z-axis of a coordinate system is subject to a constant force F is given by
`F=-hat(i) + 2hat(j)+3hat(k)` N
Where, `hat(i), hat(j), hat(k)` are unit vectors along the `x-,y-` and z axis of the system respectively. What is the work done by this force in moving the body a distance of 4m along the z-axis?

Explanation

Since the body is displaced `4m` along the z-axis only,
`S=0hati+0hatj+4hatk`
Also, `F=-i+2hatj+3hatk`
Work done,
`W=vecF.vecS=(-hati+2hatj+3hatk)*(0hati+hatj+4hatk)`
`=12(hatk.hatk)J=12J`