Question

two trains cross each other in opposite direction with velocity 72km/h. the magnitude of relative velocity of one train with respect to other is___________ km/h.​

Answer 1

Answer :-

Velocity of 1st train = 72 km/hr

As the 2nd train is in opposite direction with respect to 1st train, its velocity with respect to 1st train will ne negative.

Velocity of 2nd train = -72 km/hr

Relative velocity = Velocity of 1st train - Velocity of 2nd train

$\rm = 72 - ( - 72 )\: km/hr$

$\rm = 72 + 72 \:km/hr$

$\rm = 144 \:km/hr$

Converting it to SI unit -

$\rm 144 km/hr \times \frac{5}{18}$

$\rm = 8 \times 5 \:m/s$

$\rm = 40 \: m/s$

The magnitude of relative velocity of one train with respect to other is 144 km/hr.

Answer 2

Answer :-

Velocity of 1st train = 72 km/hr

As the 2nd train is in opposite direction with respect to 1st train, its velocity with respect to 1st train will ne negative.

Velocity of 2nd train = -72 km/hr

Relative velocity = Velocity of 1st train - Velocity of 2nd train

$\rm = 72 - ( - 72 )\: km/hr$

$\rm = 72 + 72 \:km/hr$

$\rm = 144 \:km/hr$

Converting it to SI unit -

$\rm 144 km/hr \times \frac{5}{18}$

$\rm = 8 \times 5 \:m/s$

$\rm = 40 \: m/s$

The magnitude of relative velocity of one train with respect to other is 144 km/hr.