A body falls freely from rest. It covers as much distance in the last second of its motion as covered in the first three seconds. The body has fallen for a time of……..$s$

Two stones of masses $m_1$ and $m_2$ (such that $m_1 > m_2$ ) are dropped $\Delta t$ time apart from the same height towards the ground. At a later time $t$, the difference in their speed is $\Delta v$ and their mutual separation is $\Delta \varepsilon$. While both stones are in flight

Reaction time : When a situation demands our immediate action, it takes some time before we really respond. Reaction time is the time a person takes to observe, think and act. For example, if a person is driving and suddenly a boy appears on the road, then the time elapsed before he slams the brakes of the car is the reaction time. Reaction time depends on complexity of the situation and on an individual.

You can measure your reaction time by a simple experiment. Take a ruler and ask your friend to drop it vertically through the gap between your thumb and forefinger . After you catch it, find the distance $d$ travelled by the ruler. In a particular case, $d$ was found to be $21.0\; cm$. Estimate reaction time in second.

From a building two balls $A$ and $B$ are thrown such that $A$ is thrown upwards and $B$ downwards with the same speed (both vertically). If $v_{A}$ and $v_{B}$ are their respective velocities on reaching the ground then,

A body is thrown vertically upward at $t = 0$ . It is at a height $80\,m$ at instants $t_1$ and $t_2$ . Also, it is at a height $60\,m$ at instants $t'_1$ and $t'_2$ . Then