A record turntable is rotating at 33| rev/min. A watermelon seed is on the turnt

Question

A record turntable is rotating at 33| rev/min. A watermelon seed is on the turntable 7.8 cm from the axis of rotation. (a) Calculate the acceleration of the seed, assuming that it does not slip. (b) What is the minimum value of the coefficient of static friction between the seed and the turntable if the seed is not to slip? (c) Suppose that the turntable achieves its angular speed by starting from rest and undergoing a constant angular acceleration for 0.30 s. Calculate the minimum coefficient of static friction required for the seed not to slip during the acceleration period.

Explanation / Answer

a)

angular velocity

W=(33.3*2pi/60) =3.49 rad/s

acceleration of the seed is

ac=rW2 =0.078*3.492 =0.9504 m/s2

b)

minimum value of coefficent of static friction between seed and turntable is

u=a/g =0.9504/9.81=0.09684

c)

tangential acceleration

at=0.078*(3.49/0.3) =0.9074 m/s2

a=sqrt[0.95042+0.90742]

a=1.314 m/s2

=>u=1.314/9.81=0.134

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