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PART - 1 CH - 2 Motion in a Straight Line — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysicsPART - 1 CH - 2 Motion in a Straight Line2 Marks
Question
If a person throw a ball up and catches it again after 8 sec . then tell :
(a) With what velocity was the ball thrown up?
(b) At what height will the velocity of the ball be zero?
✓

Answer

(a) It takes equal time for a ball to go up and come down.
$\therefore$ Time to go up only $=\frac{8}{2}=4 sec$.
For vertical upward,
$\begin{array}{ll}
v=u-gt & t=4(s) \\
0=u-9.8 \times 4 & u=?, v=0 m / s \\
u=39.2 m / s & g=9.8 m / s^2
\end{array}$
(b) Assume that the velocity at height h will be zero
$\begin{aligned}
v^2 & =u^2-2 gh \\
0 & =39.2 \times 39.2-2 \times 9.8 \times h \\
h & =\frac{39.2 \times 39.2}{2 \times 9.8}=78.4 \text { meter }
\end{aligned}$

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