IIT JEE , AIEEE Forum - Physics , Mechanics

tarun_896959

Given:

Two trains move with velocities 50 km/hr and 40km/hr. They move with velocities 30cm/s^2 and 20 cm/s^s.

To Find:

The time taken to cross.

SOLUTION:

30 cm/s^2 = (30/100)m/s^2 = 0.3 m/s^2

20cm/s^2 = (20/100)m/s^2 = 0.2 m/s^2

The acceleration of a body is given by a=dv/dt, dt=dv/a.

dt=[(50-40)km/hr] / [(0.3-0.2)m/s^2]

= [10km/hr] / [0.1m/s^2]

=[10*5/18 m/s] / (0.1m/s^2)

=[25/9 m/s] / [1/10 m/s^2]

=[(25*10)/(9*1)]. (m*s*s)/(m*s)

=(250/9) s

= 27.7778 s

Hence the time taken by the trains to cross each other is 27.7778 seconds.