A man is crossing a river flowing with velocity of $5\,\, m/s$. He reaches a point directly across at a distance of $60\,\, m$ in $5 \,\,sec$. His velocity in still water should be ........ $m/s$
$12$
$13$
$5$
$10$
A glass wind screen whose inclination with the vertical can be changed is mounted on a car. The car moves horizontally with a speed of $2\,\,m/s$. At what angle $\alpha$ with the vertical should the wind screen be placed so that the rain drops falling vertically downwards with velocity $6\,\, m/s$ strike the wind screen perpendicularly.
A man goes $10\,km$ downstream in $2\,hrs$ and $30\,km$ upstream in $10\,hrs$ . How much time will be take to swim $40\,km$ in still water........$hrs$
A bus appears to go with a speed of $25 \,km / hr$ to a car driver, driving at the rate $7 \,km / hr$ northwards. If the bus actually travels in east direction, its speed is ......... $km / h$
To a person, going eastward in a car with a velocity of $25\, km/hr$, a train appears to move towards north with a velocity of $25\sqrt 3 $ $km/hr$. The actual velocity of the train will be..........$km/hr$