The sum of two forces `vecP` and `vecQ` is `vecR` such that `|vecR|=|vecP|`. The angle `theta` (in degrees) that the resultant of `2vecP` and `vecQ` will make with `vecQ` is , _____________.

Answer

90

Explanation

So angle between `(2vecP+vecQ)` is `90^@`
`|vecP+vecQ|=|vecP|`
`P^2 +Q^2 +2PQ cos theta = P^2`
`implies Q + 2P cos theta =0`
`implies cos theta = -Q/(2P)`

`tan alpha=(2"P"sintheta)/(2Pcos theta+Q)=oo :. `
`[ 2P cos theta +Q=0]`
`alpha =90^@`