$A$ $100\,m$ long train crosses a man travelling at $5\,km/h$ in the opposite direction in $7.2\,s$. The velocity of the train is $..........\,km/h$.

$A$ $210 \ m$ long train is moving due North at a speed of $25 \ m/s$. $A$ small bird is flying due South a little above the train with a speed of $5 \ m/s$. The time taken by the bird to cross the train is $........ \ s$.

Two cars are moving in the same direction with a speed of $30\ km/h$. They are separated from each other by $5\ km$. $A$ third car moving in the opposite direction meets the two cars after an interval of $4\ minutes$. What is the speed of the third car in $km/h$?

Two particles $A$ and $B$ are moving along a straight line with $B$ ahead of $A$. If their velocities remain constant,what will be the effect on the magnitude of their relative velocity when $A$ is ahead of $B$?

$A$ ball is dropped from the top of a building $100\,m$ high. At the same instant,another ball is thrown upwards with a velocity of $40\,m/s$ from the bottom of the building. The two balls will meet after $..........\,s$.

$A$ $120\, m$ long train $A$ is moving with a speed of $20\, m/s$. $A$ train $B$ of length $130\, m$ is moving with a speed of $30\, m/s$ in the opposite direction. Calculate the time taken by the trains to cross each other. (in $, s$)