Question

If 2trains 18km apart are traveling towards each other 1 with a velocity of 35m/s & the other moving at 25m/s, how long would it be before the trains pass by each other?

Answer 1

Velocity of train 1, $v_1=35\space m/s$

Velocity of train 2, $v_2=25\space m/s$

Distance between the trains, $s=18\space km=18\times10^3\space m$

Assuming train 2 to be at rest relative to train 1

Relative velocity of train 1 with respect to train 2, $v_{21}=35-(-25)=60\space m/s$

Time taken by train 1 to reach train 2, $t=\dfrac{s}{v_{21}}=\dfrac{18\times10^3}{60}$

$t=300\space s=5\space min$