Work Energy And Power Ques 14
14. A body of mass $1$ $ kg$ is thrown upwards with a velocity $20$ $ m / s$. It momentarily comes to rest after attaining a height of $18$ $ m$. How much energy is lost due to air friction? $(g=10$ $m / s^{2}$ )
[2009]
(a) $30 $ $J$
(b) $40 $ $J$
(c) $10 $ $J$
(d) $20 $ $J$
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Answer:
Correct Answer: 14.(d)
Solution:
- (d) When the body is thrown upwards. its K.E is converted into P.E.
The loss of energy due to air friction is the difference of K.E and P.E.
$ \begin{aligned} \frac{1}{2} mv^{2}-mgh= & \frac{1}{2} \times 1 \times 400-1 \times 18 \times 10 \\ = \quad 200-180=20 J \end{aligned} $
BETA
