Physics quiz question: downwards trajectory vertical velocity component

Physics 205A Quiz 3, fall semester 2015
Cuesta College, San Luis Obispo, CA

A soccer ball is kicked from the ground at an angle of 35° above the horizon, with an initial horizontal velocity component of +15 m/s, such that it will hit a wall after reaching its highest point. Neglect air resistance. After reaching its highest point, but before it hits the wall, the vertical velocity component of the ball has a direction that points:
(A) upwards.
(B) downwards.
(C) (Has no direction, as the magnitude is zero.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (B)

The horizontal component of the ball's velocity never changes, while the vertical component of the ball's velocity is changing: as it moves upwards before reaching its highest point, the ball's vertical velocity component points upwards; while at the moment it is at the highest point in its trajectory, the vertical component of the ball's velocity is zero; and as it moves downwards after reaching the highest point, the vertical component of the ball's velocity points downwards.

Sections 70854, 70855, 73320
Exam code: quiz03re3T
(A) : 3 students
(B) : 55 students
(C) : 16 students
(D) : 0 students

Success level: 74%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.43