Barrons AP Calculus

BC  ONLY

vx^2 + vy^2     =   10,

(2)

vx^2 +  (2x −   1)^2 vx^2   =   10.

(3)

Relation (3) holds at all times; specifically, at (2, 2), vx^2 + 9 vx^2 = 10 so that vx =
±1. From (1), then, we see that vy = ±3. Therefore v at (2, 2) is either 1,3 or
−1,−3. The former corresponds to counterclockwise motion along the parabola,
as shown in Figure N4–19a; the latter to clockwise motion, indicated in Figure
N4–19b.

Figure  N4–19a