$A$ 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 $..........\,s$.

$A$ car is standing $200\, m$ behind a bus,which is also at rest. The two start moving at the same instant but with different forward accelerations. The bus has an acceleration of $2\, m/s^2$ and the car has an acceleration of $4\, m/s^2$. The car will catch up with the bus after a time of:

$A$ thief is running away on a straight road in a jeep moving with a speed of $9 \, m/s$. $A$ policeman chases him on a motorcycle moving at a speed of $10 \, m/s$. If the instantaneous separation between the jeep and the motorcycle is $100 \, m$,how long will it take for the policeman to catch the thief?

Two buses $A$ and $B$ are moving in opposite directions. If the first bus $A$ moves towards the east with a speed of $36 \ km/h$ and bus $B$ moves towards the west with a speed of $18 \ km/h$, then the bus $B$ appears to bus $A$ as:

Train $A$ is moving along two parallel rail tracks towards north with speed $72 \ km/h$ and train $B$ is moving towards south with speed $108 \ km/h$. The velocity of train $B$ with respect to $A$ and the velocity of the ground with respect to $B$ are (in $ms^{-1}$):

On a foggy day,two drivers spot each other when $80\, m$ apart. They were travelling at $70\, km/h$ and $60\, km/h$. Both apply brakes simultaneously which retard the cars at the rate of $5\, m/s^2$. Which of the following statements is correct?