Question

Two parallel railway track run north-south. Train A moves to north with a speed of 54 $km{h}^{-1}$ and train B moves to south with a speed of $90km{h}^{-1}$ A monkey is running on the roof of train A against its motion with a velocity of 1 8 $km{h}^{-1}$ as obtained by a person standing on the ground$.$

• A. 10 ${ms}^{-1}$
• B. 25 ${ms}^{-1}$
• C. 30 ${ms}^{-1}$
• D. 35 ${ms}^{-1}$

Answer 1

The correct option is A 10 ${ms}^{-1}$

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$,$

$VMA=VM$ $-VA$

$-5m/s=VM$ $–15m/s$

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

VM = 10 m/s$

Hence,

option $\left(A\right)$ is correct answer.