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A boy of weight 25 kg is sitting on the ...

A boy of weight 25 kg is sitting on the swing of length 5 m. A person is pulling the swing such as it makes an angle of `30^@` with the vertical. The increase in gravitational potential energy of the boy will be

A

`164.15 J`

B

`1225 J `

C

`625 J `

D

None of these

Text Solution

Verified by Experts

The correct Answer is:
A
The situation given in the question represented in the diagram given below
`cos 30^@ = (OC)/(OB) = (OC)/5`
`therefore OC = 5 cos 30^@ = 5 xx (sqrt3)/2`
`AC =OA - OC = 5 - (5sqrt(3))/(2)`
`= 5 - (5 xx 1.732)/(2)`
` = 5 - 433 = 0.67`
Now, change in potential energy = `mg(AC) `
`= 0.67 xx 25 xx 9.8 `
`= 164.15J `
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