Question

Two trains $180$ meters and $120$ meters in length are running towards each other on parallel tracks one at the rate $65$ km/hour and another at the rate of $55$ kmph. In how many seconds will they be clear of each other from the moment they meet ?

• A. 6
• B. 9
• C. 12
• D. 15

Answer 1

Answer: (B)

9

A------> 65 kmph 55 kmph <------B.

Speed of the first train:

Let $A$ is $65$ kmph and Second Train $B$ is $55$ kmph.
They run opposite to each other, then
Relative or effective speed of the Trains become,
$=65+55=120$ kmph $=\frac{120\times 5}{18}=\frac{600}{18}=\frac{100}{3}$ m/sec

Length of the first train is $180$ m and second train is $120$ m.
To cross each other, they need to cross their own length, i.e.
$(180+120=300)$ m with effective speed $\frac{100}{3}$ m/sec

<---------------180m-----------><-----------120m--------->
So, they will cover $300$ m with speed $\frac{100}{3}$ m/sec in $300\times \frac{100}{3}=\frac{300\times 3}{100}=9$ secs.