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Laws Of Motion

Question
CBSEENPH11026343

A particle slides on surface of a fixed smooth sphere starting from top most point. The angle rotated by the radius through the particle, when it leaves contact with the sphere, is

  • θ =cos-1 13

  • θ = cos-1 23

  • θ = tan-1 13

  • θ = sin-1 43

Solution

B.

θ = cos-1 23

See the diagram

   

Let the velocity be v when the body leaves the surface. From free body diagram,

                     mv2 R = mg cosθ

⇒                    v2 = R g cosθ

Again from work-energy  principle

          change in KE = work done

⇒             12 mv2 - 0 =  mg ( R -R cosθ )  

                v2 = 2gR ( 1 - cosθ)

From Eqs. (i) and (ii)

          Rg cosθ = 2gR ( 1 - cosθ )

⇒           3 gR cosθ = 2gR

⇒              θ = cos-123