Question

Two trains, each of length 100 m, move in opposite direction along parallel lines at speeds 60 km/h and 30 km/h, respectively. If their accelerations are 30 cm/s² and 20 cm/s² , respectively, then find the time they take to pass each other.

Answer 1

This problem is best solved in the reference frame of one of the trains. Find the initial relative velocity of one train with respect to the other, the relative acceleration of one train with respect to the other and the relative displacement of one train with respect to other as they pass each other. Use the second equation of motion with constant acceleration to find the required time.

The relative displacement of the trains is

S=100 + 100 = 200 M.

The initial velocity u of one train relative to the other train

Relative acceleration, a = (30+20)cm/s² = 0.5m/s² If 

't' is the time taken to cross each other,