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

A boy of weight 25kg is sitting on the swing of length 5m. 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

164.15J

B

1225J

C

625J

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- (5 sqrt3)/(2)`
`=5- (5 xx 1.732)/(2)`
`=5-422 = 0.67`
Now, change in potential energy = mg(AC)
`=0.67 xx 25 xx 9.8`
`=164.15J`
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