A block of wood of 10 kg is placed on a turntable that is rotating at 60 rpm at a distance of 1 m from the center. What is the coefficient of friction if the block does not move.  

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justaguide | College Teacher | (Level 2) Distinguished Educator

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A block of wood is placed on a turntable that is turning at 60 rpm. The mass of the block is 10 kg and it is placed at a distance of 1 m from the center of the turntable which is the point about which it is turning.

The centrifugal force exerted on the block is equal to m*w^2*R where m is the mass, w is the angular velocity and R is the distance from the center.

Substituting the values given F = 10*(2*pi)^2*1 = 394.78 N.

If the block does not move the force of friction between the turntable and the block should be equal to the centrifugal force. The frictional force is equal to C*N where C is the coefficient of friction and N is the normal force. As the block has a mass of 10 kg, the normal force is 98.1 N

Equating the two forces gives: 98.1*C = 394.78

=> C = 4.024

The value of the coefficient of friction required is 4.024.

**It should be noted that this is a very high value as a result of which the block is certainly going to move.