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?

Two trains $A$ and $B$ of length $400 \; m$ each are moving on two parallel tracks with a uniform speed of $72 \; km \; h^{-1}$ in the same direction,with $A$ ahead of $B$. The driver of $B$ decides to overtake $A$ and accelerates by $1 \; m \; s^{-2}$. If after $50 \; s$,the guard of $B$ just brushes past the driver of $A$,what was the original distance (in $m$) between them?

$A$ particle is dropped from rest and another particle is thrown downward simultaneously with initial speed $u$. Then:

$A$ man on a rectilinearly moving cart,facing the direction of motion,throws a ball straight up with respect to himself.

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 $4 \, minutes$. The speed of the third car is .......... $km/h$.

Two trains $A$ and $B$,initially $120\, km$ apart,start moving towards each other on the same track with a velocity of $60\, km/hr$ each. At the moment of start,train $A$ blows a whistle,which reflects off train $B$ and subsequently reflects off train $A$,and so on. If the velocity of sound waves in air is $1200\, km/hr$,what is the total distance travelled by the sound waves before the trains crash (in $km$)?