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2.Motion in Straight Line
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A ball is released from the top of a tower of height $h$ meters. It takes $T\, seconds$ to reach the ground. What is the position of the ball at $\frac{T}{3}\, second$
A
$\frac{{8h}}{9}$ $meters$ from the ground
B
$\frac{{7h}}{9}$ $meters$ from the ground
C
$\frac{h}{9}$ $meters$ from the ground
D
$\frac{{17h}}{{18}}$ $meters$ from the ground
(AIIMS-2012)
Solution
$\begin{array}{l}
h = \frac{1}{2}g{T^2}\\
now\,for\,t = T/3\,{\rm{second}}\,vertical\,{\rm{distance}}\,\\
moved\,is\,given\,by\\
h' = \frac{1}{2}g{\left( {\frac{T}{3}} \right)^2} \Rightarrow h' = \frac{1}{2} \times \frac{{g{T^2}}}{9} = \frac{h}{9}\\
\therefore \,Position\,of\,ball\,from\,ground\, = h – \frac{h}{9}\\
= \frac{{8h}}{9}
\end{array}$
Standard 11
Physics