Cuesta College, San Luis Obispo, CA

A Physics 205A student builds a simple pendulum using a string and a mass, and at a certain temperature it has a period of 1.50 s. As the temperature increases, determine whether the period will increase, decrease, or remain the same. Ignore friction/drag, and only consider the thermal expansion of the string. Explain your reasoning using the properties of simple harmonic motion and thermal expansion.

Solution and grading rubric:

- p:

Correct. Discusses how the period of a simple pendulum depends on the gravitational acceleration constant (which does not change) and the string length (which expands due to the increase in temperature), such that the period will increase. - r:

As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. - t:

Nearly correct, but argument has conceptual errors, or is incomplete. - v:

Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying thermal expansion to the simple pendulum parameters. - x:

Implementation/application of ideas, but credit given for effort rather than merit. Approach other than applying thermal expansion to the simple pendulum parameters. - y:

Irrelevant discussion/effectively blank. - z:

Blank.

Sections 70854, 70855, 73320

Exam code: final7rUk

p: 47 students

r: 1 students

t: 15 students

v: 6 students

x: 2 students

y: 0 students

z: 0 students

A sample "p" response (from student 5612):