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20. A penny is placed on a turntable and the table is allowed to spin. When the table reaches a certain velocity, the penny flies off. What is this velocity if, the mass of the penny is 0.0015 kg, the radius of its rotation is 0.11m, the coefficient of static friction between the penny and table is 0.40? 21. A rubber stopper is attached to the end of a string. The string is feed through a tube and a weight is hung from the other end of the string. Determine the mass of the stopper if, the hanging weight is 4.5 N, the radius of the spin is 0.8 m and the velocity of spin is 5.2 m/s. 22. The radius of mars from the sun is 2.3 x1011 m. The mass of the sun is 1.98x1030 kg. With what velocity is Mars orbiting the sun? (HINT: Set Fc = Fg and use variables first.)