$A$ $120 \, m$ long train is moving towards west with a speed of $10 \, m/s$. $A$ bird flying towards east with a speed of $5 \, m/s$ crosses the train. The time taken by the bird to cross the train will be ........ $sec$.

Two towns $A$ and $B$ are connected by a regular bus service with a bus leaving in either direction every $T$ minutes. $A$ man cycling with a speed of $20 \; km/h$ in the direction $A$ to $B$ notices that a bus goes past him every $18 \; min$ in the direction of his motion,and every $6 \; min$ in the opposite direction. What is the period $T$ (in $min$) of the bus service and with what speed (assumed constant) do the buses ply on the road?

$A$ swimmer wants to cross a $200 \ m$ wide river which is flowing at a speed of $2 \ m/s$. The velocity of the swimmer with respect to the river is $1 \ m/s$. How far from the point directly opposite to the starting point does the swimmer reach the opposite bank (in $m$)?

When is the relative velocity of two moving cars greater than the individual velocity of both cars?

$A$ girl riding a bicycle with a speed of $5 \, m/s$ towards the north direction observes rain falling vertically down. If she increases her speed to $10 \, m/s$,the rain appears to meet her at $45^o$ to the vertical. What is the speed of the rain? In what direction does the rain fall as observed by a ground-based observer?

There are two particles $P$ and $Q$ separated by a distance of $10 \ km$ and moving with velocities of $10 \ kmph$ as shown in the figure. The time elapsed before they reach their minimum separation is.........$hr$.