Physics quiz question: braking car

Physics 205A Quiz 2, fall semester 2011
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Comprehensive Problem 2.57

A car traveling at 19 m/s is brought to a full stop in 3.2 s after the brakes are applied. While braking, the car travels:
(A) 5.9 m.
(B) 30 m.
(C) 61 m.
(D) 97 m.

Correct answer: (B)

The displacement is given by:

x = 0.5·(vfx + vix)·∆t = 0.5·(0 + 19 m/s)·(3.2 s) = 30.4 m,

or 30 m with two significant figures.

Response (A) is ∆v/∆t, response (C) is ∆v·∆t, response (D) is 0.5·∆v·(∆t)2

Sections 70854, 70855
Exam code: quiz02p4iN
(A) : 6 students
(B) : 36 students
(C) : 10 students
(D) : 1 student

Success level: 68%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.56


Leah S said...

Thanks for these resources! I think there is a typo in this question. The question asks for the "average acceleration" but the answer choices offered are displacement.

Patrick M. Len said...

Dear Leah: yes, that should be displacement--I've made the correction to this post. Thanks for reading this blog!