# Two cars A and B approach a road crossing with 5m per sec and 10m per sec if angle between roads is 60 degree the relative speed of car A wrt car B is

Relative velocity of A wrt B is$\dpi{80} \vec{v_A}-\vec{v_B}$
Hence relative speed= magnitude of the relative velocity=$\dpi{80} \left|\vec{v_A}-\vec{v_B}\right|$
$\dpi{80} =\sqrt{v_A^2+v_B^2+2v_Av_Bcos60^{\circ}}=\sqrt{5^2+10^2+2(5)(10)\dfrac{1}{2}}=\sqrt{175}m/s$