Question

a train whose length is 120 M is moving at a speed of 90 km per hour another train whose length is 180 M is moving on parallel rails in the opposite direction at a speed of 72 km per hour find how long the first in will takes to pass 1) the second train in 20/3 sec

Answer 1

Given
Length of train 1=120m
Speed=90km/hr

Let change the speed in m/s first

1km/hr=5/18 m/s


Then speed of 1st train becomes =90x5/18 =25m/s


Similarly

Length of 2nd train =180

Speed=72km/s =72x5/18 =20m/s



Now total distance to cover = length of 1st train + length of 2nd train

D=120+180

=300m


Trains are moving in opposite direction then according to the relative velocity

Relative speed=speed of 1st train + speed of 2nd train

S=25+20=45m/s

Time required to cross=D/S

=300/45

=100/15

$= \frac{20}{3} m \: per \: sec$

This is ur ans hope it will help you in case of any doubt comment below