Question

Two trains of lengths $120$ m and $90$ m are running with speed of $80$ km/hr and $55$ km/hr respectively towards each other on parallel lines. If they are $90$ m apart, after how many seconds they will cross each other completely?

• A. $5.6$ sec
• B. $7.2$ sec
• C. $8$ sec
• D. $9$ sec

Answer 1

The correct option is C $8$ sec

As the trains are running in opposite direction,
relative speed $=80+55=135$ km/hr $=135\times \frac{5}{18}=\frac{75}{2}$ m/s

Distance covered $=(120+90+90)=300$ m
$\therefore$ Required time $=\frac{300\times 2}{75}=8$ sec