Question:

A stone is tied to a string of length 'l' and is whirled in a vertical circle with the other end of the string as the center. At a certain instant of time, the stone is at its lowest position and has a speed of 'u'. The magnitude of the change in velocity as it reaches a position where the string is horizontal (g being acceleration due to gravity) is

Updated On: Oct 7, 2023
  • \(\sqrt{u^2-gl}\)

  • \(u-\sqrt{u^2-2gl}\)

  • \(\sqrt{2gl}\)

  • \(\sqrt{2(u^2-gl)}\)

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The Correct Option is D

Solution and Explanation

The magnitude of the change in velocity as a stone reaches a position where the string is horizontal, starting from its lowest point with speed 'u', is 2u.
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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.