An old wheat-grinding wheel in a museum actually works. The sign on the wall says that the wheel has a rotational acceleration of 210 rad/s2 as its spinning rotational speed increases from zero to 1700 rpm . Part A How long does it take the wheel to attain this rotational speed?

Iknow the first part it is the average star i am not 100% sure

Answer(a)   the matererials that are in contact, the two materials and the nature of their surfaces/// (b)/// the force pushing the two surfaces together, pushing the surfaces together causes the more of the asperities to come together and increases the surface area in contact with each other