A bullet losses 1/n of its velocity in passing through a plank. What i...
Solution:
Introduction:
When a bullet passes through a plank, it loses 1/n of its velocity. We need to find the minimum number of planks required to stop the bullet.
Concept:
The velocity of the bullet decreases by a factor of 1/n after passing through each plank. We can use the formula for velocity after a certain distance covered with constant retardation, V² - U² = 2as, where V is the final velocity, U is the initial velocity, a is the retardation, and s is the distance covered.
Calculation:
Let the initial velocity of the bullet be U. After passing through the first plank, the velocity becomes U/n. To stop the bullet, the final velocity should be zero. Therefore, the distance covered by the bullet after passing through the first plank is given by:
(U/n)² - U² = -2as
On simplifying, we get:
s = (n² - 1)U²/2an²
The bullet has to pass through n planks. Therefore, the total distance covered by the bullet is:
S = n((n² - 1)U²/2an²)
We need to find the minimum value of n such that S is greater than or equal to the thickness of the planks.
Conclusion:
In conclusion, the minimum number of planks required to stop the bullet is given by:
n = √((U²t)/(2a(U²/n² - U²)))
where t is the thickness of the plank.