A man throws the bricks to a height of 12 m where they reach with a speed of `12 m//s`. If he throws the bricks such that they just reach that height, what percentage of energy will be saved? `(g = 9.8 m//s^(2))`

Options

A. `9.5%`
B. `19%`
C. `38%`
D. `76%`

Answer

C

Explanation

In first Case, `W_(1) = 1/2m(v_(1))^(2) + mgh`
`=1/2m(12)^(2) + m xx 10 xx 12`
=72m + 120 m
and in second case, `W_(2)` = mgh
=120 m
The percentage of energy saved
`=(192m - 120m)/(192m) xx 100 = 38%`