Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 4.22
Students were asked the following clicker questions (Classroom Performance System, einstruction.com) in the middle of their learning cycle:
A 2,010 kg elevator moves with an upward acceleration of 1.50 m/s^2.
Which force has the least magnitude?
(A) Net force on the elevator.
(B) Weight of the elevator.
(C) Tension force of cable on the elevator.
(D) (There is a tie.)
(E) (I'm lost, and don't know how to answer this.)
Sections 30880, 30881
(A) : 29 students
(B) : 11 students
(C) : 0 students
(D) : 0 students
(E) : 1 student
(F) : 0 students
This question was asked again after displaying the tallied results with the lack of consensus, with the following results. No comments were made by the instructor, in order to see if students were going to be able to discuss and determine the correct answer among themselves.
Sections 30880, 30881
(A) : 37 students
(B) : 6 students
(C) : 0 students
(D) : 0 students
(E) : 0 students
(F) : 0 students
Correct answer: (A)
The free-body diagram for the elevator is discussed in a previous post:
Physics clicker question: accelerating elevator free-body diagrams
The weight force is given by m*g = 1.97e4 N, upwards. The net force, from Newton's second law, is m*a = 3.02e3 N, upwards. Thus the magnitude of the upwards tension force must be greater than the weight force by 3.02e3 N, which must then be 2.27e4 N, making it the force with the greatest magnitude, and of these three choices, net force has the least magnitude.
Pre- to post- peer-interaction gains:
pre-interaction correct = 71%
post-interaction correct = 86%
Hake, or normalized gain
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