Stick the circle mechanics

a stick of mass density 'Q' per unit length rests on a circle of radius 'R' . the stick makes an angle θ \theta 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
- θ \theta is 60 degrees

Q Q/5 32.14Q 5Q

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1 solution

Mark Hennings
Mar 19, 2018

Considering first the forces on the circle, taking moment about the centre O 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 F + F \cos60^\circ \; = \; R_2\cos30^\circ and hence R 2 = F 3 R_2 = F\sqrt{3} .

Now considering forces on the rod, taking moments about X X tells us that R 2 × L = W 1 × 1 2 L cos 6 0 R_2\times L \; = \; W_1 \times \tfrac12L \cos60^\circ and hence R 2 = 1 4 W 1 R_2 = \tfrac14W_1 , and hence F = W 1 4 3 F = \tfrac{W_1}{4\sqrt3} , where L = 2 3 L = 2\sqrt{3} is the length of the rod, and W 1 = Q L g W_1 = QLg is the weight of the rod. Thus F = 1 2 Q g = 5 Q F = \tfrac12Qg = \boxed{5Q} .

Interestingly, resolving forces on the rod horizontally tells us that F 3 = F F_3 = F as well.

i'm sorry but what is R? Is it a normal force?

Steffannie Colynx - 10 months, 3 weeks ago

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Yes, they are the normal reactions.

Mark Hennings - 10 months, 3 weeks ago

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