Physics quiz question: aircraft carrier steam catapult

Physics 205A Quiz 4, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 7.7

"F/A-18E-F Super Hornet Catapult Launches"
AiirSource
youtu.be/BHdz9hcccpw

A steam catapult on an aircraft carrier can launch a stationary airplane (mass 20,000 kg) to a speed of 74 m/s in 2.0 s[*]. The magnitude of the impulse exerted on the airplane is:
(A) 37 N·s.
(B) 7.4×10⁵ N·s.
(C) 1.5×10⁶ N·s.
(D) 5.5×10⁷ N·s.

[*] "45,000-pound plane from 0 to 165 miles per hour in two seconds," science.howstuffworks.com/aircraft-carrier3.htm.

Correct answer (highlight to unhide): (C)

The impulse J can be calculated as the initial-to-final change in momentum:

J = ∆p = m·∆v,

where ∆v = v_f – v₀, and assuming that the plane is moving in the +x direction after being catapulted (such that v_f = +74 m/s):

J = (20,000 kg)((+74 m/s) – (0 m/s)) = +1,480,000 N·s,

or to two significant figures, the magnitude of the impulse on the plane is 1.5×10⁶ N·s.

(Response (A) is the magnitude of the acceleration, response (B) is the magnitude of the net force, response (D) is the initial kinetic energy.)

Sections 70854, 70855
Exam code: quiz04Bmw3
(A) : 2 students
(B) : 16 students
(C) : 32 students
(D) : 2 students

Success level: 62%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.87