A bullet loses $\frac{1}{20}$ of its velocity after penetrating a plank. How many planks are required to stop the bullet?

9

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11

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7

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5

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Solution

The correct option is B $11$
Energy lost after passing through one plank = $\frac{m v^{2}}{2} - m (\frac{19 v}{20})^{2}$

No. of planks it require to pass through to loose complete energy
= $\frac{T o t a l I n i t i a l E n e r g y}{E n e r g y l o s t t h r o u g h o n e p l a n k} ≃ 10.25$

So minimum no. of planks required = 11

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Similar questions

A bullet loses $\frac{1}{20}$ of its velocity in passing through a plank. The least number of planks required to stop the bullet is

(\frac{1}{n})^{t h}

1 / 20^{t h}

\frac{1}{20}

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