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2.Motion in Straight Line
easy
A boy throws balls into air at regular interval of $2$ second. The next ball is thrown when the velocity of first ball is zero. How high do the ball rise above his hand is ...... $m$ [Take $g=9.8 \,m / s ^2$ ]
A
$4.9$
B
$9.8$
C
$19.6$
D
$29.4$
Solution

(c)
$2 T=\frac{2 u}{g} \Rightarrow 2=\frac{u}{9.8} \Rightarrow u=19.6$
$H=\frac{u^2}{2 g}=\frac{19.6 \times 19.6}{2 \times 9.8}$
$\Rightarrow H=19.6 \,m$
Standard 11
Physics