Physics midterm question: vector addition

Physics 205A Midterm 1, fall semester 2011
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 3.21(b)

Two vectors P and Q, are added such that P + Q = R. What is the magnitude of vector R?
(A) 4 units.
(B) 7 units.
(C) 8 units.
(D) 10 units.

Correct answer: (B)

Vectors P and Q have x and y components of (-4,0) and (+3,+7) respectively. The resultant vector R will then be (-1,+7), such that the magnitude will be given by:

|R| = sqrt((-1)^2 + (+7)^2) = sqrt(1 + 49) = sqrt(50) = 7.07106781,

or to one significant figure, 7.

Sections 70854, 70855
Exam code: midterm01w4Sh
(A) : 0 students
(B) : 36 students
(C) : 15 students
(D) : 2 students

Success level: 68%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.53