Calculating Forces and Angles in a Model Plane System

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The discussion focuses on calculating the forces and angles in a motorized model plane system. The central force acting on the plane is determined using the formula Fc = mrω², resulting in a value of 2.52 N. To find the angle θ of the string to the vertical, the tangent function is applied, yielding an angle of 52°. The calculations are confirmed as accurate and satisfactory. This analysis demonstrates the application of physics principles to model circular motion.
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Homework Statement


A motorised model plane is attached to a light string anchored to a ceiling. The plane follows a circular path of radius 0∙35 m as shown in Figure 2.
upload_2016-1-18_15-48-44.png

The plane has a mass of 0∙20 kg and moves with a constant angular velocity of 6∙0 rad s−1 .

(a) Calculate the central force acting on the plane.
(b) Calculate the angle θ of the string to the vertical.

2. Homework Equations

Fc = mrω2

The Attempt at a Solution


a)Fc = mrω2
0.2 x 0.35 x 6.02
= 2.52N

b) tanθ = Fc/Fw
tanθ = 2.52/(0.2x9.8)
θ = tan-1(2.52/0.2x9.8)
θ = 52°
 

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The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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