## 20121025

### 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 = vfv0, and assuming that the plane is moving in the +x direction after being catapulted (such that vf = +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