Question

A train $150m$ long passes a pole in $15s$ time, and it takes $8s$ to pass another train of the same length travelling in opposite direction. What is the speed of the second train?

• A. 60 km/hr
• B. 66 km/hr
• C. 72 km/hr
• D. 99 km/hr

Answer 1

Answer: (D)

Speed of first train $= \, \left(\frac{150}{15}\right)\frac{m}{s e c} \, = \, 10\frac{m}{s e c}$
Let the speed of second train be x m/sec.
Relative speed $= \, \left(10 \, + \, x\right)\frac{m}{s e c} \, $ .
$\therefore $ $\frac{300}{10 + x}=8\Leftrightarrow 300 \, = \, 80 \, + \, 8x \, \Leftrightarrow x=\frac{220}{5}=\frac{55}{2}\frac{m}{s e c}$ .
So, speed of second train $= \, \left(\frac{55}{2} \times \frac{18}{5}\right) \, kmph \, = \, 99 \, kmph$ .