Two forces and act simultaneously on a particle

MATHEMATICS · Single correct · A Level · Mathematics · Vectors · Vectors

Problem

Two forces

\mathbf{F}_1=8\,\hat\imath+k\,\hat\jmath\,\text{N}

and

\mathbf{F}_2=-5\,\hat\imath+6\,\hat\jmath\,\text{N}

act simultaneously on a particle. If the resultant is perpendicular to

\mathbf{F}_2

, the value of

k

is (a)

6.67

(b)

3.5

(c)

-3.5

(d)

2.5