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A child is swinging a swing. Minimum and...

A child is swinging a swing. Minimum and maximum heights fo swing from the earth's surface are 0.75 m and 2 m respectively. The maximum velocity of this swing is

A

5m/s

B

15m/s

C

10 m/s

D

20 m/s

Text Solution

Verified by Experts

The correct Answer is:
A
At the bottom it has only K.E. `=(1)/(2)mv^(2)` and at the height point, it has only P.E. = mgh.
`therefore` Loss in energy
= K.E. at the bottom = P.E. at the highest point
`=(1)/(2)mv^(2)-mgh`
`=(1)/(2)xx1xx400-1xx10xx18`
`=200-180=20J`
This loss in energy is due to resistance of air.
`therefore` Loss of energy due to air friction = 20 J
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