Question

A train is moving southwards at a speed of 30 ms–1. A monkey is running northwards on the roof of the train with a speed of 5ms–1. What is the velocity of the monkey as obserced by a person standing on the ground?

Solution

Correct option is

25 ms–1 in the southward direction

Suppose we choose the direction from south to north as the positive direction. Then the velocity of the train moving southwards = –30 ms–1. Velocity of the monkey running northwards = +5 ms–1. Therefore, the velocity of the monkey as observed by a person in the ground = –30 + 5 = –25 ms–1. The negative sign indicates that the direction of this velocity is southwards.

SIMILAR QUESTIONS

Q1

A man wants to reach point B on the opposite bank of a river flowing at a speed. What minimum speed relative to water should the man have so that he can reach point B. In which direction should he swim?

Q2

A train is moving eastwards with a velocity of 10 m/sec. On a parallel track another train passes with a velocity 15 m/sec eastwards. To the passengers in the second train the first train appears to be moving with a velocity.

Q3

A man can swim at a speed of 3 km/hr in still water. He wants to cross a 500 m wide river flowing at 2 km/hr. He keeps himself always at angle of 120o with the river flow when swimming find the time he takes to cross the river.

Q4

A jet airplane traveling from east to west at a speed of 500 kmh–1 ejects out gases of combustion at a speed of 1500 kmh–1 with respect to the jet plane. What is the velocity of the gases with respect to an observer on the ground?   

 

Q5

A police van moving on a highway with a speed of 36 km h–1 fires a bullet at a thief’s car speeding away in the same direction with a speed of 108 km h–1. If the muzzle speed of the bullet is 140 ms–1, with what speed will the bullet hit the thief’s car?    

Q6

Car A is moving with a speed of 36 km h–1 on a two-lane road. Two carsB and C, each moving with a speed of 54 km h–1 in opposite direction on the other lane are approaching car A. At a certain instant when the distance AB = distance AC = 1 km, the diver of car B decides to overtakeA before C does. What must be the minimum acceleration of car B so as to avoid an accident?   

Q7

The driver of a train A moving at a speed of 30 ms–1 sights another trainB moving on the same track at a speed of 10 ms–1 in the same direction. He immediately applies brakes and achieves a uniform retardation of 2 ms–1. To avoid collision, what must be the minimum distance between the trains?      

Q8

The driver of a train A moving at a speed of 30 ms–1 sights another trainB moving on the same tack towards his train at a speed of 10 ms–1. He immediately applies brakes and achieves a uniform retardation of 4 ms–2. To avoid head-on collision, what must be the minimum distance between the trains?