Concept:In a smooth conical funnel, the normal reaction's horizontal component provides the centripetal force, while its vertical component balances the weight.
Explanation:Let the particle move in a horizontal circle of radius
r at a height
h from the vertex of the funnel.
Let
α be the semi-vertical angle of the cone.
The forces acting on the particle are its weight
mg and the normal reaction
N.
From the geometry of the cone,
tanα=hr.
The horizontal component of
N is
Ncosα, and the vertical component is
Nsinα.
Thus,
NsinαNcosα=rh.
For horizontal circular motion:
Ncosα=rmv2For vertical equilibrium:
Nsinα=mgDividing these two equations:
rgv2=rhCancelling
r from both sides:
h=gv2Substituting
v=0.5m/s and
g=10m/s2:
h=10(0.5)2=100.25=0.025mConverting into centimetres:
h=0.025m=2.5cmAnswer:The height of the plane of the circle from the vertex is
2.5cm.
Correct option: B.