# A bullet of mass 20 g has an initial speed of $1 ms^{-1} ,$ just before its starts penetrating a mud wall of thickness 20 cm . If the wall offers a mean resistance of $2.5 \times 10 ^{-2} N$ , the speed of the bullet after emerging from the other side of the wall is close to : Option 1)$0.1 ms^{-1}$Option 2)$0.7 ms^{-1}$Option 3)$0.3 ms^{-1}$Option 4)$0.4 ms^{-1}$

Given ,

$m = 20 \times 10 ^{-3} Kg , U = 1 m/s \\\\ S = 20 \times 10 ^{-2} m \\\\ a = - \frac{2.5 \times 10 ^{-2}}{20 \times 10 ^{-3}} m /s ^2$

$V^2 = U^2 + 2 as \\\\ V^2 = 1 ^ 2 - 2 \times \frac{2.5 \times 10 ^{-2}}{20 \times 10 ^{-3}} \times \frac{20}{100} \\\\ V^2 = 1/2 \\\\ V = 1 / \sqrt 2 \\\\ V = 0.7 m/s$

Option 1)

$0.1 ms^{-1}$

Option 2)

$0.7 ms^{-1}$

Option 3)

$0.3 ms^{-1}$

Option 4)

$0.4 ms^{-1}$

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