Physics quiz question: basketball vertical velocity component

Physics 205A Quiz 3, fall semester 2018
Cuesta College, San Luis Obispo, CA

A Physics 205A student throws a basketball with an initial velocity vector that has x- and y-components:

v_0x = +5.5 m/s,
v_0y = +4.2 m/s.

Neglect air resistance. At the highest point in its trajectory, the magnitude of the basketball's vertical velocity is:
(A) 0 m/s.
(B) some value between 0 m/s and 4.2 m/s.
(C) 4.2 m/s.
(D) some value greater than 4.2 m/s.

Correct answer (highlight to unhide): (A)

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
Exam code: quiz03pRH5
(A) : 37 students
(B) : 4 students
(C) : 9 students
(D) : 6 students

Success level: 66%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.67