Two cars start at the same time from in point and move alone two roads, at right angle to each other. The speeds are 36 km/hr and 48 km/hr respectively. After 15 sec distance between them will be :

Answer: Option D

Distance travelled by the 1st car in 15 seconds
$$\begin{array}{rl}& \text{OA}=\left(36\times \frac{5}{18}\right)\times 15\text{m}\\ & =150\text{m}\end{array}$$
Distance travelled by the 2nd car in 15 seconds
$$\begin{array}{rl}& \text{OB}=\left(48\times \frac{5}{18}\right)\times 15\text{m}\\ & =200\text{m}\end{array}$$
∴ Distance between them after 15 seconds
$$\begin{array}{rl}& \text{AB}=\sqrt{\text{O}{\text{A}}^2+\text{O}{\text{B}}^2}\\ & =\sqrt{{150}^2+{200}^2}\\ & =\sqrt{22500+40000}\\ & =\sqrt{62500}\\ & =250\text{m}\end{array}$$