(1 point) An object with weight W is dragged along a horizontal plane by a force acting along a rope attached to the object. If the rope makes an angle t W with the plane, then the magnitude of the force is F = u, where u is a constant called the coefficient of friction. Let W = 15 lb and p sm t + cos t [4 = 0.4. (a) Find the rate of change of F with respect to t. W) = C] 0)) When is this rate of change equal to zero? Round your answer to the nearest hundredth. t=Drad