Question

A bus $60$ m long passes a girl, running at $3$ km/hr in the same direction in which the bus is going, in $6$ seconds. Then the speed of the bus is

• A. $39$ km/hr
• B. $30$ km/hr
• C. $33$ km/hr
• D. $42$ km/hr

Answer 1

The correct option is A $39$ km/hr

Speed of the bus relative to the girl
$=\frac{60}{6}=10$ m/sec
$=10\times \frac{18}{5}=36$ km/hr
Let the speed of the bus relative to ground be $x.$
Then, relative speed $=(x-3)$ km/hr
$\Rightarrow 36=x-3$
$\Rightarrow x=39$ km/hr
Hence, the speed of the bus is $39$ km/hr.