A bullet of mass 20 g moving with a velocity of 500 m/s, strikes a tree and goes out from the other side with a velocity of 400 m/s. Calculate the work done by the bullet (in joules) in passing through the tree.

900 J

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800 J

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950 J

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500 J

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Solution

The correct option is A $900 J$
Given, mass of the bullet, $m = 20 g = 0.02 k g$ ;
initial velocity of the bullet, $u = 500 m / s$ ;
final velocity of the bullet, $v = 400 m / s$
Work done by the tree against the bullet,

$W_{t r e e} = \frac{1}{2} m v^{2} - \frac{1}{2} m v^{2} = \frac{1}{2} m (v^{2} - u^{2})$

$= \frac{1}{2} (0.02) [(400)^{2} - (500)^{2}] = - 900 J$

Work done by the bullet, $W_{b u l l e t} = - W_{t r e e}$
or $W_{b u l l e t} = - (- 900 J) = 900 J$

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