Physics 5A Quiz 2, Fall Semester 2007
Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 2.43
[3.0 points.] A brick is thrown and released vertically upward with an initial speed of 2.00 m/s from the top ledge of a building, 12.0 m above ground level. The brick reaches its highest height, then moves downwards to strike the ground. Take upwards to be the positive vertical direction. With what speed does the brick strike the ground?
(A) 10.8 m/s.
(B) 11.0 m/s.
(C) 15.3 m/s.
(D) 15.5 m/s.
Correct answer: (D)
Since time is not explicitly given, the most direct approach is to solve for v_f,y using:
(v_fy)^2 - (v_iy)^2 = 2*a_y*delta(y),
where v_iy = +2.00 m/s, a_y = -9.80 m/s^2, and delta(y) = -12.0 m.
Response (C) is using v_iy = 0 (this was the most common error). Response (B) is leaving out the factor of 2. Response (A) is the result of both errors in responses (C) and (B).
Student responses
Sections 0906, 0907
(A) : 1 student
(B) : 5 students
(C) : 20 students
(D) : 16 students
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