$A$ 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 $s$)

$A$ train is moving towards the east and a car is moving towards the north,both with the same speed. The observed direction of the car to a passenger in the train is

On a calm day,a boat can go across a lake and return in time $T_0$ at a speed $V$. On a rough day,there is a uniform current at speed $v$ that helps the onward journey and impedes the return journey. If the time taken to go across and return on the rough day is $T$,then $T / T_0$ is:

On a two-lane road,car $A$ is travelling with a speed of $36 \; km/h$. Two cars $B$ and $C$ approach car $A$ in opposite directions with a speed of $54 \; km/h$ each. At a certain instant,when the distance $AB = AC = 1 \; km$,car $B$ decides to overtake car $A$ before car $C$ does. What minimum acceleration (in $m/s^2$) of car $B$ is required to avoid an accident?

$A$ swimmer can swim in still water with $5 \,m/s$. If a river is flowing with $4 \,m/s$, then find the time to cross the river of width $300 \,m$ if he has to reach the exactly opposite point.

$A$ bird is flying to and fro between two cars moving towards each other on a straight road. One car has a speed of $18\,km/h$ while the other has a speed of $27\,km/h$. The bird starts moving from the first car towards the other with a speed of $36\,km/h$. If the two cars were initially separated by $36\,km$,what is the total distance covered by the bird?