A) A spring scale on a rotating platform indicates that the horizontal force on

Question

A) A spring scale on a rotating platform indicates that the horizontal force on a 0.476 kg mass is 1.47 N when the mass is 2.04 m from the axis of rotation. How long does it take for the platform to make one revolution?

B) A coin placed on a turntable rotating at 32.2 rev/min will stay there if its center is placed no further than 9.4 cm from the axis of rotation. -What is the maximum distance the center of the coin can be placed from the axis if the turntable rotates at 45.5 rev/min?

-What is the coefficient of friction between the coin and turntable?

Explanation / Answer

A)

F = mr2 [as v = r]
= F/mr
= [1.47/(0.476 x 2.04)
= 1.23rad/sec
2/T = 1.23
T = (2 x 3.14)/1.23
T = 5.105sec

B)

The frictional force is the centripetal force

So F max = m*r*2

Now Fmax/m is a constant

so we have r1*12 = r2*22

or r2 = r1*(1/2)2

= 9.4cm*(32.2/45.5)2

= 4.707cm

-µ*m*g = m*r*2

so

µ = r*2/g

= 0.094*(32.2*2/60)2/9.8

= 0.108

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