1). Is the acceleration of a projectile equal to zero when it reaches the top of its trajectory? I know that when a projectile reaches the top of its trajectory, v=0 because velocity is momentarily horizontal. However, how would I relate this to acceleration? 2). A tennis ball is hit into the air and moves along an arc. Ignoring air resistance, where along the arc is the speed of the ball at its minimum and maximum? Why? Would it be correct to say that speed is at a minimum at the top of the arc and at a maximum as the arc goes downward? 3). A wrench is dropped from the top of the mast on a sailboat. Will the wrench hit at the same place on the deck, whether the sailboat is at rest or moving with a constant velocity? I'm completely stuck on this one. ^^;; Any pointers in the right direction would be greatly appreciated. Thanks in advance for the help!