Question

Water drops fall from a tap on to the floor $5.0$ m below at regular intervals of time. The first drop strikes the floor when the fifth drop beings to fall. The height at which the third drop will be from ground, at the instant when the first drop strikes the ground is (Take $g=10m{s}^{-2}$):

• A. $1.25m$
• B. $2.15m$
• C. $2.75m$
• D. $3.75m$

Answer 1

The correct option is D $3.75m$

First we final the time taken by $1^{st}$ drop to fall.

$t=\sqrt{\frac{2H}{g}}=\sqrt{\frac{2\times 5}{10}}=1s$

Now in an interval of 1 sec, $5^{th}$ drop is falling.

$\Rightarrow$Interval b/w each drop is $0.25s$

So, $3^{rd}$ drop will fall after $0.5s$

Hence $s_3=\frac{1}{2}g(1-0.5{)}^2=\frac{9}{8}=1.25m$

Distance from ground $=5-1.25=3.75m$