Kinematics

JEE Main level, single correct, medium

62 of 308

Question 62 of 308

A bullet of mass 20g20g has an initial speed of 1ms−11m{s}^{-1}, just before it starts penetrating a mud wall of thickness 20cm20cm. If the wall offers a mean resistance of 2.5×10−2N,2.5\times {10}^{-2}N, the speed of the bullet after emerging from the other side of the wall is close to:

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Answer: (A) 0.7ms−10.7m{s}^{-1}

a=−2.5×10−220×10−3=−54ms−2a=-\dfrac{2.5\times {10}^{-2}}{20\times {10}^{-3}}=-\dfrac{5}{4}m{s}^{-2}
From v2−u2=2as{v}^{2}-{u}^{2}=2as
v2=u2+2as{v}^{2}={u}^{2}+2as
v=12−2×54×20×10−2v=\sqrt{{1}^{2}-2\times \dfrac{5}{4}\times 20\times {10}^{-2}}
=0.5=\sqrt{0.5}
=0.7ms−1=0.7m{s}^{-1}

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