$A$ river is flowing from west to east with a speed of $9 \ km \ h^{-1}$. $A$ boat, capable of moving at a maximum speed of $27 \ km \ h^{-1}$ in still water, crosses the river in half a minute. If the boat moves at an angle of $150^{\circ}$ to the direction of the river flow, then the width of the river is:

$A$ moves with $65 \, km/h$ while $B$ is moving in the same direction as $A$ with $80 \, km/h$. The relative velocity of $B$ with respect to $A$ is ......... $km/h$.

Train $A$ and train $B$ are running on parallel tracks in opposite directions with speeds of $36 \, km/h$ and $72 \, km/h$,respectively. $A$ person is walking in train $A$ in the direction opposite to its motion with a speed of $1.8 \, km/h$. The speed (in $m/s$) of this person as observed from train $B$ will be close to:
(take the distance between the tracks as negligible) (in $.5$)

$A$ $120 \, m$ 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 particles having position vectors $r_1 = (3 \hat{i} + 5 \hat{j}) \text{ m}$ and $r_2 = (-5 \hat{i} - 3 \hat{j}) \text{ m}$ are moving with velocities $v_1 = (4 \hat{i} + 3 \hat{j}) \text{ m/s}$ and $v_2 = (a \hat{i} + 7 \hat{j}) \text{ m/s}$. If they collide after $2 \text{ s}$,then the value of $a$ is:

$A$ 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 second car with a speed of $36 \,km/h$ when the two cars are separated by $36 \,km$. What is the total distance covered by the bird?