$A$ stone is dropped from a certain height and reaches the ground in $5\, s$. If the stone is stopped after $3\, s$ of its fall and then allowed to fall again,then the time taken by the stone to reach the ground for the remaining distance is........$s$.

It is a common observation that rain clouds can be at about a kilometer altitude above the ground.
$(a)$ If a rain drop falls from such a height freely under gravity,what will be its speed? Also calculate in $km/h$ $(g = 10\, m/s^2)$.
$(b)$ $A$ typical rain drop is about $4\, mm$ in diameter. Momentum is mass $\times$ speed in magnitude. Estimate its momentum when it hits the ground.
$(c)$ Estimate the time required to flatten the drop.
$(d)$ Rate of change of momentum is force. Estimate how much force such a drop would exert on you.
$(e)$ Estimate the order of magnitude force on an umbrella. Typical lateral separation between two rain drops is $5\, cm$.
(Assume that the umbrella is circular and has a diameter of $1\, m$ and the cloth is not pierced through.)

When a ball is thrown up vertically with velocity $V_o$,it reaches a maximum height of $h$. If one wishes to triple the maximum height,then the ball should be thrown with what velocity?

Four marbles are dropped from the top of a tower one after the other with an interval of one second. The first one reaches the ground after $4$ seconds. When the first one reaches the ground,the distances between the first and second,the second and third,and the third and fourth marbles will be respectively:

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 the 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 the reaction time in seconds. (in $; s$)

Water drops are falling from a nozzle of a shower onto the floor,from a height of $9.8\, m$. The drops fall at a regular interval of time. When the first drop strikes the floor,at that instant,the third drop begins to fall. Locate the position of the second drop from the floor when the first drop strikes the floor. (In $m$)