A record turntable is rotating at 33 1/3 rev/min. A watermelon seed is on the turntable 6.8 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 0.35 s. Calculate the minimum coefficient of static friction required for the seed not to slip during the acceleration period.

Part (a) I found by finding the radial component of the acceleration, a_r, by using the angular velocity squared times the radius, with the units properly converted to get it to m/s

Part (b) I found by setting the force of static friction equal to the force acting on the seed, mu_k*g*m=a_r*m, and solved for mu_k.

Part (c) I am lost on.