Question

Two parallel rail tracks run north – south. Train A moves North with a speed of 54 km /h and train B

moves South with a speed of 90 km/ h what is the relative velocity of B with respect to A.(ii). relative

velocity of B with respect to ground .(iii) velocity of a monkey running on the roof of the train A

against its motion (with a velocity of 18 km /h with respect to the trainA) as observed by a man

standing on the ground​

Answer 1

Answer:

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Answer 2

Explanation:

We have,,

Consider North direction as +ve direction and South as -ve,,

Velocity of train A w.r.t. ground, $\sf{\blue{V_{AG}=+54 \:kmh^{-1}=+15 \:ms^{-1}}}$ due North

Velocity of train B w.r.t. ground, $\sf{\blue{V_{BG}=-90\: kmh^{-1}=-25 \:ms^{-1}}}$ due South

(i)

Therefore, velocity of B w.r.t. A is given by,

$\sf{V_{BA}=V_{BG} - V_{AG}}$

$\sf{\implies{V_{BA}=(-25 - 15)\:ms^{-1}}}$

$\implies{\boxed{\sf{V_{BA}=-40\:ms^{-1}}}}$

(ii)

Thus, velocity of train B w.r.t. ground is given by,

$\boxed{\sf{V_{BG}=-25 \:ms^{-1}}}$

(iii)

Since, monkey is running against the train A and we have velocity of monkey w.r.t. train A,

$\sf{\blue{V_{MA}=-18 \:kmh^{-1}=-5\:ms^{-1}}}$

Now, velocity of monkey as observed by a man standing on the ground is given by,

$\sf{V_{MG}=V_{MA}+V_{AG}}$

$\sf{\implies{V_{MG}=-5+15}}$

$\implies{\boxed{\sf{V_{MG}=10\: ms^{-1}}}}$

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