Walker, Halliday & Resnick — Motion in Two and Three Dimensions: Problem 17

17 A motorbike starts from the origin and moves over an xy plane with acceleration components $a_x = 6.0 \text{ m/s}^2$ and $a_y = -3.0 \text{ m/s}^2$. The initial velocity of the motorbike has components $v_{0x} = 12.0 \text{ m/s}$ and $v_{0y} = 18.0 \text{ m/s}$. Find the velocity of the motorbike, in unit-vector notation, when it reaches its greatest y coordinate.