Question

a body of mass m kg is rotating in a verical circle at end of string of length r metre. The difference in KE at top and bottom of circle is-

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Answer 1

answer:

Considering no external force other than gravity, the difference in kinetic energies is due to change in potential energy which is mgh.

Here h=2r. So, change in kinetic energies is 2mgr.

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Answer 2

Answer:

The difference in Kinetic Energy at the top and bottom of the circle is 2mgr.

Explanation:

The change in the kinetic energy = The change in potential energy.

P.E = mxgxh (m= mass, g = acceleration due to gravity), h = height.

ΔK.E = Δ P.E = mg(h1 - h2)  ............. (1)

Radius of circle = r

Therefore, h1 - h2 = 2r ( diameter of a circle = 2 X radius)

On substituting, the value in (1)

ΔK.E  = mg X 2r

Thus, the difference in the energy is 2mgr.

• Kinetic energy is a form of energy that an object or a particle has by reason of its motion. If work, which transfers energy, is done on an object by applying a net force, the object speeds up and thereby gains kinetic energy.

Examples: Any object in motion is using kinetic energy:

• a person walking, a thrown baseball,
• a crumb falling from a table,
• a charged particle in an electric field is an example of kinetic energy at work.

• Potential energy, stored energy that depends upon the relative position of various parts of a system.

Examples:

• Spring has more potential energy when it is compressed or stretched.
• A steel ball has more potential energy raised above the ground than it has after falling to Earth.