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.


Correct option is


             Vr1g = velocity of the river with respect to the ground

           Vm1r = velocity of the man with respect to the river

          Vm1g = velocity of the man with respect to the ground

We have, 

Hence, the velocity with respected to ground is along the AC. Taking y components in eq. 1.  








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?


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.


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?


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?   



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?