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Physics quiz question: comparing wire vs. string wave speeds

Physics 205A Quiz 6, fall semester 2008
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 11.6, Multiple-Choice Question 11.5

A string and a wire are each 10.0 m long, and are stretched by the same tension of 30.0 N. The string has a mass of 2.40×10–3 kg, and the wire has a mass of 1.90×10–3 kg.

Waves will travel faster along the:
(A) string.
(B) wire.
(C) (There is a tie.)
(D) (Not enough information is given to determine this.)

Correct answer (highlight to unhide): (B)

Transverse waves on a string or wire is given by v = √(F/(m/L)), where both strings have the same tension F, but have different linear mass densities ("thicknesses") (m/L). Since the wire has a smaller mass per length, waves will travel faster along it.

Student responses
Sections 70854, 70855
(A) : 3 students
(B) : 34 students
(C) : 2 students
(D) : 0 students

Success level: 92%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.21

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