Physics clicker question: airbag effect

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

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Example 7.3

Students were asked the following clicker question (Classroom Performance System, einstruction.com) in the middle of their learning cycle:

[0.6 participation points.] An airbag (in conjunction with a seatbelt) will lessen the injuries caused by a car accident. How does the airbag do this, compared to wearing a seatbelt only?
(A) By decreasing the change in momentum.
(B) By decreasing the amount of impulse.
(C) By increasing the time duration of impact.
(D) (More than one of the above choices apply.)
(E) (I'm lost, and don't know how to answer this.)

Sections 0906, 0907
(A) : 5 students
(B) : 5 students
(C) : 11 students
(D) : 14 students
(E) : 0 students

Correct answer: (C)
Assuming that the same type of accident is involved for the same mass occupant, the momentum change (m*(v_f - v_i) will be the same, as will be the impulse on the driver. The time duration (delta_t) for the impulse (F*delta_t) to be applied will be longer with the airbag, thus the force applied on the occupant will be lessened.