Question

Two parallel train tracks run north-south. Train A runs towards north with a speed 54km/hr and train B towards south with a speed of 90km/hr. Calculate relative speed of a monkey running on the roof of train A against the motion of the train with a velocity 18km/hr as observed by a person standing on the ground.

Answer 1

Solution - 

Velocity of Monkey with respect to ground is – VM

Velocity of Monkey with respect to train A is - VA

Relative velocity of Monkey with respect to train A - VMA

VMA = VM - VA

Given - Velocity of Monkey with respect to train A = VA = 54 Km/h = 54 x 5/18 m/s = 15 m/s

And Relative velocity of Monkey with respect to train A = VMA = -18 Km/h = -18 x 5/18 = -5 m/s

(as monkey running against the motion)

Therefore,

VMA = VM - VA

-5 m/s = VM – 15 m/s

VM = -5 m/s + 15 m/s

VM = 10 m/s

Answer - The velocity of a monkey running on roof of a train A against its motion is 10 m/s