13. Let r1 = (15, 152) and r2 = (215, t2+1) be parametric curves describing the trajectories of two objects. (a) Compute the distance between the two objects at t = 3. (b) Show that the trajectories of the objects intersect, but show that the two objects do not collide. (c) Adjust the speed of r1 so that the two objects collide. (d) (Continuation of last part) What is the angle of impact? what is the speed of the two objects upon impact? 14. (Choosing the order for computing higher partial derivatives.) Consider the function ./ 1/3 . f (say) = sin(%#) + my. Since f is innitely differentiable, fmy = fym. However, computing the partial derivatives in one order is a lot of work and the other is not. Try to compute the mixed partial derivative in both orders. (Always keep on the look out for an easier order.)