20160927

Physics quiz question: horizontal velocity component of upwards-kicked soccer ball

Physics 205A Quiz 3, fall semester 2016
Cuesta College, San Luis Obispo, CA

A soccer ball is kicked from ground level with an upwards angle, with initial horizontal and vertical velocity components of 
v0x = +2.8 m/s, 
v0y = +10.6 m/s, respectively. Neglect air resistance. After the soccer ball was kicked, but just before it reaches its highest point above the ground, the magnitude of the horizontal velocity component of the ball:
(A) decreases.
(B) remains constant.
(C) increases.
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (B)

For the ideal case of projectile motion were air resistance is negligible, the vertical component of the ball's velocity continuously changes (due to the downwards vertical acceleration due to gravity), while the horizontal component of the ball's velocity never changes (due to there being no horizontal acceleration).

Sections 70854, 70855, 73320
Exam code: quiz03sHO7
(A) : 9 students
(B) : 42 students
(C) : 6 students
(D) : 0 students

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

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