Physics quiz question: marshmallow compression

Physics 205A Quiz 6, fall semester 2018
Cuesta College, San Luis Obispo, CA

A marshmallow has a height of 3.8×10^–2 m, a circular cross-sectional area of 5.1×10^–4 m², and a Young's modulus of 2.9×10⁴ N/m².[*][**] A downwards force of 10 N is applied evenly onto the top of the marshmallow. As a result, the marshmallow is compressed by:
(A) 6.7×10^–9 m.
(B) 1.3×10^–5 m.
(C) 2.6×10^–2 m.
(D) 2.0×10⁴ m.

[*] amazon.com/ask/questions/Tx21SLNIPLG0WI4.
[**] physics.info/elasticity/.

Correct answer (highlight to unhide): (C)

Hooke's law is given by:

(F/A) = Y·(∆L/L),

such that the amount that the marshmallow would be compressed is:

∆L = (F·L)/(A·Y),

∆L = ((10 N)·(3.8×10^–2 m))/((5.1×10^–4 m²)·(2.9×10⁴ N/m²)),

∆L = 0.02569303584... m,

or to two significant figures, the marshmallow would compress by 2.6×10^–2 m.

(Response (A) is (F·L·A)/Y; response (B) is F·L/Y; response (D) is the stress F/A.)

Sections 70854, 70855
Exam code: quiz06POr7
(A) : 4 students
(B) : 3 students
(C) : 43 students
(D) : 2 students

Success level: 83%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.50