First slide
Vectors
Question

The sum of the magnitudes of two forces acting at a point is 18 and the magnitude of their resultant is 12. If the resultant is at 90° with the force of smaller magnitude, what are the magnitudes of forces?

Moderate
Solution

We have, P + Q = 18

and R= 12

Qsinθ=P and Qcosθ=R

Squaring and adding, we get

P2 +R2 = Q2

or Q2 - P2 = R2 = 144

Solving Eqs. (i) and (ii) , we get

P = 5 and Q = 13.

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