Maximum Static Friction Force for Spinning Disk and Block System

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The discussion focuses on calculating the maximum rate of rotation for a spinning disk system involving a penny and a block, considering the static and kinetic friction coefficients. The static friction force is crucial in preventing the penny from sliding off the block as the disk spins. The participants emphasize understanding the maximum static friction force that can act on both the penny and the block. The solution involves applying the relevant equations of motion and friction to determine the critical rotational speed. Ultimately, the goal is to find the maximum revolutions per minute without any sliding occurring between the objects.
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Homework Statement


A penny of mass 3.10g rests on a small 20.0g block supported by a spinning disk. The coefficients of friciton between block and disk are .750(static) and 0.640(kinetic) while those for the penny and block are 0.520(static) and .450(kinetic). What is the maximum rate of rotation in revolutions per minute that the dsk can have, without the block or penny sliding on the disk?


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The Attempt at a Solution

 
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What force prevents the penny from sliding?
 
static friction
 
I think I can solve this problem now thanks
 
Right. So what's the maximum force that static friction can exert on each object?
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
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