A bullet of mass 0.1 kg is fired on a wooden block to pierce through it, but it stops after moving a distance of 50 cm into it. If the velocity of bullet before hitting the wood is $10 \mathrm{~m} / \mathrm{s}$ and slows down with uniform deceleration, then magnitude effective retarding force on the bullet is 'x' N. The value of 'x' to the nearest integer is ______

JEE Main · 2021 · 18 Mar 2021 · Shift 1 · Laws of Motion

A bullet of mass 0.1 kg is fired on a wooden block to pierce through it, but it stops after moving a distance of 50 cm into it. If the velocity of bullet before hitting the wood is

10 m / s

and slows down with uniform deceleration, then magnitude effective retarding force on the bullet is 'x' N.
The value of 'x' to the nearest integer is ______

Answer: 10

Solution

Inside the block the retarding force is the only force doing work on the bullet, so the work it does equals the whole kinetic energy lost:

F d = \frac{1}{2} m v^{2}

F \times 0.5 = \frac{1}{2} \times 0.1 \times (10)^{2} = 5 J

The magnitude of the effective retarding force is

10

JEE Main · 2021 · 18 Mar 2021 · Shift 1 · Integer answer

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