SATHEE: Work Energy And Power Question 40

Work Energy And Power Question 40

Question: A rifle bullet loses 1/20th of its velocity in passing through a plank. The least number of such planks required just to stop the bullet is [EAMCET 1987; AFMC 2004]

Options:

A) 5

B) 10

C) 11

D) 20

Show Answer

Answer:

Correct Answer: C

Solution:

Let the thickness of one plank is s if bullet enters with velocity u then it leaves with velocity $v = (u - \frac{u}{20}) = \frac{19}{20} u$ from $v^{2} = u^{2} - 2 a s$

therefore ${(\frac{19}{20} u)}^{2} = u^{2} - 2 a s$

therefore $\frac{400}{39} = \frac{u^{2}}{2 a s}$

Now if the n planks are arranged just to stop the bullet then again from $v^{2} = u^{2} - 2 a s$

$0 = u^{2} - 2 a n s$

therefore $n = \frac{u^{2}}{2 a s} = \frac{400}{39}$

therefore $n = 10.25$ As the planks are more than 10 so we can consider n = 11

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Work Energy And Power Question 40

Question: A rifle bullet loses 1/20th of its velocity in passing through a plank. The least number of such planks required just to stop the bullet is [EAMCET 1987; AFMC 2004]

Options:

Answer:

Solution:

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