Physics clicker question: circular motion free-body diagrams

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

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 5.38

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

Use these free-body diagrams for the following questions:


[0.6 participation points.] Which free-body diagram represents a passenger (upside-down) at the top of a vertical loop, traveling fast enough that there is still contact with the seat?

Sections 0906, 0907
(A) : 1 student
(B) : 10 students
(C) : 10 students
(D) : 9 students
(E) : 1 student
(F) : 8 students

Correct answer: (F)
At the top of the circular arc, the net force points inwards (downwards), which is comprised of both the downwards normal force of the seat on the passenger, and the weight force of the Earth on the passenger.

[0.6 participation points.] Which free-body diagram represents a passenger (upside-down) at the top of a vertical loop, traveling just fast enough that there is barely contact with the seat?

Sections 0906, 0907
(A) : 0 students
(B) : 0 students
(C) : 2 students
(D) : 1 student
(E) : 35 student
(F) : 1 student

Correct answer: (E)
At the top of the circular arc, the net force points inwards (downwards), which is comprised only the downwards weight force of the Earth on the passenger.