Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 10.30
Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the end of their learning cycle:
A 0.40 kg object on a 99 N/m spring oscillates left to right on a frictionless surface, with an amplitude of 0.10 m. What is the speed of the object at the equilibrium point?
(A) 0 m/s.
(B) 0.40 m/s.
(C) 1.57 m/s.
(D) 24.8 m/s.
(E) (I'm lost, and don't know how to answer this.)
Sections 30880, 30881
(A) : 2 students
(B) : 14 students
(C) : 9 students
(D) : 3 students
(E) : 4 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) : 1 student
(B) : 19 students
(C) : 0 students
(D) : 0 students
(E) : 5 students
Correct answer: (C)
From energy conservation, the potential energy of the mass when the spring is fully compressed or stretched at its maximum displacement from equilibrium x = +/- A can be set equal to the kinetic energy of the mass as it passes through equilibrium at x = 0:
U_max = K_max,
(1/2)*k*A^2 = (1/2)*m*v_max^2,
such that v_max = sqrt(k/m). Response (B) is the period T = 2*pi*sqrt(m/k) of this mass-spring system, and (D) is the maximum acceleration a_max = (k/m*)*A.
Pre- to post- peer-interaction gains:
pre-interaction correct = 28%
post-interaction correct = 0%
Hake, or normalized gain
No comments:
Post a Comment