A car on a hill of constant slope accelerates from rest under gravity to a point on the hill. If you want to maximize the velocity of the car at this point, where along the length of the car (e.g. downhill or uphill) would you fix an additional mass?

Hint: What fundamental dynamics equation governs this situation?

(a) the finishing point is on the slope of the hill
(b) the finishing point is on a flat below the slope of the hill.