Question

a body is acted upon by a force f=-12i+5j work done by the force in moving the body from the origin to a point, coordinates of which are (5,4)

Answer 1

We know that, Work done by a constant force is given by :
W = F. s
s = Position vector of point wrt initial point.

Here,
F = -12i + 5j
s = (5-0)i + (4-0)k = 5i + 4j
W = F. s.
= -12 * 5 + 5 * 4
= -60 + 20
= -40Joules .
Hence, Work Done required is -40J.

Negative Sign indicates angle between Force vector and displacement vector is obtuse.