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A man throws the bricks to a height of 1...

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))`

A

0.29

B

0.46

C

0.38

D

0.5

Text Solution

Verified by Experts

The correct Answer is:
C
According to the question, the energy of bricks,
`E_(1) mgh+ (1)/(2) mv^(2) , E_(2) = mgh`
Energy saved, `Delta E= E_(1) - E_(2) = (1)/(2) mv^(2) `
Percentage of saved energy `= (Delta E)/( E_1) xx 100`
`= ((1)/(2) mv^(2) )/(mgh+ (1)/(2) mv^(2) ) xx 100 = (v^2) /( 2 gh + v^(2) ) xx 100`
`= ((12)^2)/( 2 (9.8) 12 + (12)^2) =(144)/(235.2 + 144) xx 100`
`=37.97 = 38%`
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