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A body of mass 1 kg is thrown upwards wi...

A body of mass `1 kg` is thrown upwards with a velocity `20 ms^(-1)`. It momentarily comes to rest after attaining a height of `18 m`. How much energy is lost due to air friction? `(g = 10 ms^(-2))`

A

20J

B

10J

C

30J

D

40J

Text Solution

Verified by Experts

The correct Answer is:
A
Loss in `P.E.=mg(h_(1)-h_(2))`
where, `h_(1)=100m, h_(2)=20m`
We do not consider the intermediate height of 30 m.

Gain in `K.E.=(1)/(2)mv^(2)`
`therefore (1)/(2)mv^(2)=mg(h_(1)-h_(2))`
`therefore v=sqrt(2g(h_(1)-h_(2)))`
`= sqrt(2xx10xx(100-20))=sqrt(1600)=40m//s`
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