a stick of mass density 'Q' per unit length rests on a circle of radius 'R' . the stick makes an angle
with the horizontal and is tangent to the circle at its upper end . Friction exists at all points of contact and assume that it it is large enough to keep the system at rest . Find frictional force between ground and circle.
- radius is 2 m and
- take g's value as 10 .......... 9.8 will not give correct answer
-
is 60 degrees
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Considering first the forces on the circle, taking moment about the centre O tells us that the frictional forces at the two points of contact are the same. Resolving forces horizontally gives F + F cos 6 0 ∘ = R 2 cos 3 0 ∘ and hence R 2 = F 3 .
Now considering forces on the rod, taking moments about X tells us that R 2 × L = W 1 × 2 1 L cos 6 0 ∘ and hence R 2 = 4 1 W 1 , and hence F = 4 3 W 1 , where L = 2 3 is the length of the rod, and W 1 = Q L g is the weight of the rod. Thus F = 2 1 Q g = 5 Q .
Interestingly, resolving forces on the rod horizontally tells us that F 3 = F as well.