Thank you for reporting, we will resolve it shortly
Q.
The resultant of two forces $P$ and $Q$ is of magnitude $P$. If the force $P$ is doubled , $Q$ remaining the same, then angle between new resultant and the force $Q$ is
Let the angle between $P$ and $Q$ be $\alpha$ .
Then as resultant of $P$ and $Q$ is $P$.
$\Rightarrow P^{2}=P^{2}+Q^{2}+2PQ\, \cos\,\alpha$
$0=Q+2P\, \cos\,\alpha $
Let $^{\theta}$ be the angle which the new resultant makes with $Q$
Then $\tan\,\theta=2P\, \sin\,\alpha /\left(Q+2P\, \cos\,\alpha \right)-1 / 0=\infty$
$\Rightarrow \theta =90^{0}$