Question

the resultant of two forces P and Q is of magnitude P. IF P be doubled the resultant will be inclined to angle Q at an angle?

Answer 1

The resultant of P⃗ P→and Q⃗ Q→ is P⃗ +Q⃗ P→+Q→and dot product with P⃗ P→is 0.0.

So

(P⃗ +Q⃗ )⋅(P⃗ )=0P2+Q⃗ ⋅P⃗ =0|P|2+|P||Q|cosθ=0|P|+|Q|cosθ=0cosθ=−|P||Q|