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A ball of mass 200g is attached to a str...


A ball of mass `200g` is attached to a string of length `50cm` and a force `F` is applied on it as shown. Find the work done by this force if string makes an angle `60^@` with vertical. In the initial and final position, speed of the ball is zero.

Text Solution

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`K_i=0`,`K_f=0`
`W=K_f-K_i`
`W_T+W_(gr)+W_F=W=K_f-K_i=0`
`W_T=0` (since tension is always perpendicular to displacement)
`W_(gr)=-mgL(1-cos60^@)`
`=-0.2xx10xx0.5xx(1)/(2)=-0.5J`
Work done by force `F`, `W_F=0.5J`
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