11. A block weighing 75 lbs. sits on an inclined plane where the coefficient of friction is 0.45. a. If the angle is 40.0, will the block slide down on its own? b. What would it take to drag the block up the hill at a constant speed? Extra Credit. them formula A 0.180-kg rock is stuck between the tires of a semi-truck. The coefficient of friction for rubber tire against the rocks is 0.70. If the force squeezing together is 45 N, how fast do the .65 m radius wheels need to be spinning before the rock flies from the wheels? This requires you to look up the for centripetal force (which we have not yet discussed.).