Physics clicker question: ball thrown-down versus ball thrown horizontally

Physics 10, Winter Quarter 2009
University of California, San Diego, CA

Cf. Hewitt, Conceptual Physics, 10/e

Students were asked the following clicker question (Interwrite Personal Response System, interwritelearning.com) in the middle of their learning cycle:

Consider a pair of identical cannonballs about to be simultaneously thrown with the same speed from the same height. Ball A is shot horizontally from a cannon. Ball B is thrown vertically downward by a person. Which will hit the ground first?
(A) Ball A.
(B) Ball B.
(C) They will hit at the exact same time.

Section 642701
(A) : 1 student
(B) : 30 students
(C) : 76 students

This question was asked at the end of the class; so there was no more time for follow-up questions or discussion.

Correct answer: (B)

Presumably students misread the question, confusing it with a situation where the first ball was released from rest rather than being thrown down.

(Question and statistics courtesy of Dr. Michael G. Anderson, Department of Physics, University of California, San Diego, CA.)