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BITSAT 2021 Paper

Section: Physics

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Question : 16 of 150

Marks: +1, -0

A ball of mass

0.2\,\text{kg}

is thrown vertically upwards by applying a force by hand. If the hand moves

0.2\,\text{m}

while applying the force and the ball goes upto

2\,\text{m}

height further, find the magnitude of the force. (Consider

\text{g}=10\,\text{m}/\text{s}^{2}

$4\,\text{N}$
$16\,\text{N}$
$20\,\text{N}$
$22\,\text{N}$

Solution:

Let the velocity of the ball just when it leaves the hand is u then applying,

v^{2}-u^{2}=2 a s

for upward journey

⇒

-u^{2} = 2(-10) \times 2

\Rightarrow u^{2} = 40

Again applying

v^{2}-u^{2}=2 a s

for the upward journey of the ball, when the ball is in the hands of the thrower,

v^{2}-u^{2}=2 a s

⇒

40-0=2(a) 0.2

\Rightarrow a=100\,\text{m}/\text{s}^{2}

∴

F=m a=0.2 \times 100=20\,\text{N}

⇒

N-m g=20

\Rightarrow N=20+2=22\,\text{N}

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