A ball is thrown vertically upwards which attains a maximum height of $20 m$ . Calculate the velocity with which the ball is thrown upwards? (Take $g = 9.8 m s^{- 2}$ )

29.79 m s^{- 1}

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17.79 m s^{- 1}

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19.79 m s^{- 1}

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15.79 m s^{- 1}

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Solution

The correct option is C $19.79 m s^{- 1}$
Let initial velocity of ball be $u$
Distance travelled, $s = 20 m$
Final velocity, $v = 0 m s^{- 1}$
Acceleration due to gravity, $g = 9.8 m s^{- 2}$
Acceleration of the ball, $a = - 9.8 m s^{- 2}$
( $∵$ motion is in upwards direction)
Using third equation of motion,
$v^{2}$ = $u^{2}$ + $2 a s$
$0 = u^{2} + 2 \times (- 9.8) \times 20$
$u^{2} = 392$
$⟹ u = 19.79 m s^{- 1}$
Hence, the ball is thrown with velocity $19.79 m s^{- 1}$

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A ball is thrown vertically upwards which attains a maximum height of 20 m. Calculate the velocity with which the ball is thrown upwards? (Take g=9.8 m s−2)

A ball is thrown vertically upwards which attains a maximum height of $20 m$ . Calculate the velocity with which the ball is thrown upwards? (Take $g = 9.8 m s^{- 2}$ )