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))`

Options

A. `20 J`
B. `30 J`
C. `40 J`
D. `10 J`

Answer

`(1)`

Explanation

Intial velocity `u = 20 m /s, m = 1 kg`
Kinetic energy = maximum potential energy
Initial kinetic energy = `1/2 xx 1 xx 20^(2) = 200 J`
`Mgh(max) = 200 J`
`therefore h = 20 m`. The height travelled by the body, h. = 18m `Rightarrow` Energy lost =` 200 J - 1 xx10 xx18 J = 20J`