Question

Two vectors of magnitude 3 units and 4 units respectively. What should be the angle between them if the magnitude of the resultant is 7 units ?

• A. ${180}^o$
• B. $0^o$
• C. ${90}^o$
• D. ${60}^o$

Answer 1

The correct option is B $0^o$

We know that magnitude of resultant vector of $\overline{A}$ and $\overline{B}$ =$\sqrt{A^2+B^2+2ABcos\left(\theta \right)}$,

$\Rightarrow 49=9+16+2\times 3\times 4\times cos\left(\theta \right)$,

$\Rightarrow cos\left(\theta \right)=1$ $\Rightarrow \theta =0^o$.