Question

A train consisting of $30$ wagons each of mass $15$ tonnes is pulled by an engine of power $90kW$. If the frictional force and air resistive force offered per tonne of the train is $12N$. Find the maximum velocity with which the train can travel.

• A. $40kmph$
• B. $60kmph$
• C. $80kmph$
• D. $100kmph$

Answer 1

The correct option is B $60kmph$

The frictional force and air resistive force offered per tonne of the train is $12N$
For $15$ tonnes,
$f=12\times 15=180N$
Now,
For $30$ wagons the total frictional force,
$f=30\times 180=5400N$
We know,
$P=f\times v$
$\therefore v=\frac{P}{f}$
$\therefore v=\frac{90\times {10}^3}{5400}$
$\therefore v=16.67m/s$
$\therefore v=60kmph$