$A$ boat takes $2 \, h$ to travel $8 \, km$ and back in still water. If the velocity of water is $4 \, km/h$,the time taken for going upstream $8 \, km$ and coming back is:

$A$ person walks up a stalled escalator in $90 \ s$. When standing on the same moving escalator,he reaches the top in $60 \ s$. The time it would take him to walk up the moving escalator will be: (in $s$)

$A$ person aiming to reach the exactly opposite point on the bank of a stream is swimming with a speed of $0.5\, m/s$ at an angle of $120^\circ$ with the direction of flow of water. The speed of water in the stream is..........$m/s$.

The maximum speed of a boat in still water is $27 \,km/h$. Now this boat is moving downstream in a river flowing at $9 \,km/h$. $A$ man in the boat throws a ball vertically upwards with a speed of $10 \,m/s$. The range of the ball as observed by an observer at rest on the river bank is . . . . . . $cm$. (Take $g = 10 \,m/s^2$)

$A$ man crosses a $320 \ m$ wide river perpendicular to the current in $4 \ minutes$. If in still water he can swim with a speed $5/3$ times that of the current,then the speed of the current,in $m/min$ is

$A$ girl standing on a road holds her umbrella at $45^{\circ}$ with the vertical to keep the rain away. If she starts running without an umbrella with a speed of $15 \sqrt{2} \; kmh^{-1}$,the rain drops hit her head vertically. The speed of rain drops with respect to the moving girl is ........... $kmh^{-1}$