A ball is thrown from a roof top at an angle of 45o above the horizontal. It hits the ground a few seconds later. At what point during its motion, does the ball have a) greatest speed b) smallest speed c) greatest acceleration?
a) Assume the ball is thrown $45^o$ from O. The ball’s height increases from O to A, lowering its KE. The speed increases as the height lowers from A to B, until it reaches the initial speed when the ball was at O. O and B are on the same horizontal line. From B to C, speed increases as height decreases. So $v_y$ max at C and $v_x$ = u/2. B) Point A has the slowest speed since the height is highest and vy = 0 because the horizontal speed is constant (ie; u/2). c) The greatest acceleration is attributable to gravity, as only gravity acts downward on the ball.
