Question

Two trains $160$ m and $140$ m long are running in opposite directions on parallel rails. The first at $77$ km/hr and the other at $67$ km/hr. How long will they take to cross each other ?

• A. $7$ seconds
• B. $7\frac{1}{2}$ seconds
• C. $6$ seconds
• D. $10$ seconds

Answer 1

Answer: (B)

$7\frac{1}{2}$ seconds

Since the two trains are moving in opposite direction the relative speed of the faster train w.r.t the slower train $=$ Sum of their speeds
$=(77+67)$ km/hr $=144$ km/hr $=$ $(144\times \frac{5}{18})$ m/sec $=40$ m/sec
Distance travelled $=$ Sum of the lengths of the two trains $=160$ m $+$ $140$ m $=300$ m
$\therefore$ Required time $=$ $\frac{300m}{40m/sec}=7\frac{1}{2}$ sec