A body dropped from a height H reaches t...

A body dropped from a height H reaches the ground with a speed of 1.2 `sqrt(gH)`. Calculate the work done by air friction.

A

`0.14mgH`

B

`0.28mgH`

C

`-0.14mgH`

D

`-0.28mgH`

Text Solution

Verified by Experts

The correct Answer is:

D

`K_1+U_1=K_2+U_2+W_f`
`W_f`: work done against friction
`0+mgH=(1)/(20mv^2+0+W_f`
`mgH=(1)/(2)m(1.44)gH+W_f`
`W_f=0.28mgH`
Work done by friction `W_f^(')=-W_f=0.28mgH`

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