Question:

A disc of mass $100\, g$ is kept floating horizontally in air by firing bullets, each of mass $5\, g$ with the same velocity at the same rate of $10$ bullets per second. The bullets rebound with the same speed in opposite direction, the velocity of each bullet at the time of impact is:

Updated On: Jul 12, 2022
  • 196 cm/s
  • 9.8 cm/s
  • 98 cm/s
  • 980 cm/s
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The Correct Option is D

Solution and Explanation

From law of conservation of momentum Total momentum of bullets $=$ Momentum of disc $2 m' \eta n=m g$ $v=\frac{m g}{2 m' n} =\frac{100 \times 980}{2 \times 5 \times 10}$ $=980 \,cm / s$
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Notes on laws of motion

Concepts Used:

Laws of Motion

The laws of motion, which are the keystone of classical mechanics, are three statements that defined the relationships between the forces acting on a body and its motion. They were first disclosed by English physicist and mathematician Isaac Newton.

Newton’s First Law of Motion

Newton’s 1st law states that a body at rest or uniform motion will continue to be at rest or uniform motion until and unless a net external force acts on it.

Newton’s Second Law of Motion

Newton's 2nd law of motion deals with the relation between force and acceleration. According to the second law of motion, the acceleration of an object as built by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

Newton’s Third Law of Motion

Newton's 3rd law of motion states when a body applies a force on another body that there is an equal and opposite reaction for every action.