Physics quiz question: soccer ball trajectory time

Physics 205A Quiz 3, fall semester 2014
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Conceptual Question 3.9

A soccer ball is kicked from the ground at an upward angle, such it lands back on the horizontal ground a distance of 35 m downrange, 1.7 s later. Neglect air resistance. If kicked with the same initial vertical speed, but with a slower initial horizontal speed, the ball will land back on the ground __________ later.
(A) less than 1.7 s.
(B) 1.7 s.
(C) more than 1.7 s.
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (B)

The initial vertical speed of the soccer ball determines the time it will be in flight, independently of the (initial) horizontal speed of the soccer ball. (Note that the slower initial horizontal speed for the soccer ball means that it will travel a shorter horizontal distance during this same amount of time, when it lands downrange.)

Sections 70854, 70855, 73320
Exam code: quiz03fkfs
(A) : 26 students
(B) : 33 students
(C) : 13 students
(D) : 0 students

Success level: 46%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.73