Gujarat BoardEnglish MediumSTD 9ScienceGravitation3 Marks
Question
A ball thrown up vertically returns to the thrower after $6s$. Findthe velocity with which it was thrown up.
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Answer
Time of ascent is equal to the time of descent. The ball takes a total of $6s$ for its upward and downward journey.
Hence, it has taken 3s to attain the maximum height.
Final velocity of the ball at the maximum height, $v = 0$
Acceleration due to gravity, $g = -9.8m s^{-2}$
Equation of motion, $v = u +$ gt will give,
$0 = u + (-9.8 \times 3)$
$u = 9.8 \times 3 = 29.4m s^{-1}$
Hence, the ball was thrown upwards with a velocity of $29.4m s^{-1}$.
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