Physics quiz question: impulse-driven objects

Physics 5A Quiz 4, Fall Semester 2007
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Conceptual Question 7.2(b)

[Version 1]

[3.0 points.] An impulse of 50 N*s is applied to each of two objects of different masses that are initially at rest. Which object has the greatest velocity change?
(A) The less massive object.
(B) The more massive object.
(C) (Both objects have the same velocity change.)
(D) (Not enough information is given to determine this.)

Correct answer: (A)

Impulse = delta(p) = m*(v_f - v_i). With v_i = 0 for both objects, v_f will be greater for the less massive object, and v_f will be smaller for the more massive object.

Student responses
Sections 0906, 0907
(A) : 15 students
(B) : 4 students
(C) : 2 students
(D) : 0 students

[Version 2]

[3.0 points.] Two objects of different masses are initially at rest, and then undergo the same velocity change. Which object experienced the greater impulse?
(A) The less massive object.
(B) The more massive object.
(C) (Both objects experienced the same impulse.)
(D) (Not enough information is given to determine this.)

Correct answer: (B)

Impulse = delta(p) = m*(v_f - v_i). With v_i = 0 for both objects, and the same v_f as well, a greater impulse would be exerted on the more massive object, and a smaller impulse would be exerted on the less massive object.

Student responses
Sections 0906, 0907
(A) : 5 students
(B) : 13 students
(C) : 1 student
(D) : 0 students