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Friday, November 16, 2012

Q.458. Circular Motion under gravity

Question 458.
A particle moves from rest at point A on the surface of a smooth circular cylinder of radius R. At B the particle leaves the cylinder. Find the equation relating θ1 and θ2.

Answer 458.
Potential energy at A = mgRcosθ1
Potential energy at B = mgRsinθ2
Gain of kinetic energy = loss of potential energy
=> (1/2) mv^2 = mgR (cosθ1 - sinθ2)
=> mv^2/R = 2mg (cosθ1 - sinθ2) ... ( 1 )

At point B, the particle will lose contact if the centripetal force = radial component of weight
=> mv^2/R = mgsinθ2 ... ( 2 )

From ( 1 ) and ( 2 ),
mgsinθ2 = 2mg (cosθ1 - sinθ2)
=> 2cosθ1 - 3sinθ2 = 0.

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