The image shows the trajectory of baseball, with four labelled positions A throu

Question

The image shows the trajectory of baseball, with four labelled positions A through D. Positions A and C are at the same height, position B is at the highest point of the trajectory, and position D is shortly before the player catches the ball. Neglect air resistance for this problem.

Which one of the following statements is true?
The vertical component of the velocity is the same at points A and C.
The ball has maximum speed at point D.
The ball has zero acceleration at point B.
The vertical component of the acceleration changes sign at point B.
The ball has zero velocity at point B.

Explanation / Answer

Vox = constant = horizontal speed of ball = 6.9 m/s
h = 1/2gt² {where h = 10.6 - 1.9 = 8.7 m
t = 2h/g = (17.4/9.81) = 1.7737 = 1.332 s {time for ball to reach its max height above release height}
Voy = vertical component of speed of ball at release height (also catch height) = gt = (9.81)(1.332) = 13.1 m/s
final speed when caught (position D) = (Vox²+Voy²) = (6.9²+13.1²) = 219.22 = 14.8 m/s

The speed of the ball at point A is the same as at point C

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