Physics quiz question: pilot in looping airplane

Physics 8A Quiz 4, Spring Semester 2007
Cuesta College, San Luis Obispo, CA

Physics 8A learning goal Q4.4

[3.0 points.] An airplane flies in a loop (a circular path in a vertical plane) of radius 200 m. The pilot's head always points toward the center of the loop. The speed of the airplane is not constant; the airplane goes slowest at the top of the loop, and fastest at the bottom. Which one of the free-body diagrams (A)-(F) best corresponds to forces acting on the pilot when she is at the bottom of the loop? The forces on these diagrams are unlabeled, but are drawn approximately to scale. Clearly circle your answer.



(Cf. Young and Freeman, University Physics, 11/e, Exercise 5.51.)

Correct answer: (C)
Choices (B) and (D) are zero net force cases, while choices (E) and (F) have net forces that point downwards. By process of elimination, the only remaining choices are (A) and (C), which have net forces that point upwards, which is radially inwards when the pilot is at the bottom of the loop. There are two forces that act on the pilot, the weight force of the Earth on the pilot (downwards), and the normal force of the seat on the pilot (upwards), with the normal force having a (much) larger magnitude than the weight force.

Student responses:
(A) : 3 students
(B) : 10 students
(C) : 14 students
(D) : 2 students
(E) : 1 student
(F) : 4 students