Question

The resultant of two vectors `vec(P)` and `vec(Q)` is `vec(R )`. If the magnitude of `vec(Q)` is doubled, the new resultant vector becomes perpendicular to `vec(P)`. Then, the magnitude of `vec(R )` is equal to
A. P + Q
B. P
C. P - Q
D. Q

Answer 1

Correct Answer - 4
`tan90^(@)=(2Qsintheta)/(p+2Qcostheta)`

`impliesP+2Qcostheta=0`
`& R^(2)=P^(2)+Q^(2)+2PQcostheta`
`=Q^(2)+P(P+2Qcostheta)`
`=Q^(2)+0`
`impliesR=Q`