Rain is falling vertically with a speed of 4 ms–1. After some time, wind starts blowing with a speed of 3 ms–1 in the north to south direction. In order to protect himself from rain, a man standing on the ground should hold his umbrella at an angle  given by


Correct option is

 with the vertical towards north


Velocity of rain (vr) = 4 ms–1 vertically downwards. Velocity of wind  from north to south direction. A rain drop is acted upon by two velocities vr and vw. From the triangle law, the resultant velocity of the rain drop is v = OW. In order to protect himself from rain, he must hold his umbrella at an angle  with the vertical (towards north) given by 






A 120 metre long train is moving west at a speed of 10 ms–1. A small bird flying east at a speed of 5 ms–1 crosses the train. What is the time taken by the bird to across the train?


A swimmer can swim in still water with a speed of 5 ms–1. While crossing a river his average speed is 3 ms–1. If he crosses the river in the shortest possible time, what is the speed of flow of water?