G.C. Sloan: Physics 2305, Exam 3

Physics 2305: Exam 3 Results

As usual, letter grades assigned to exams are for comparitive purposes only; they aren't used to determine final course grades.

Answer keys are below

Students: 237

Mean: 63.6

Std Dev: 19.9

A 34

B 58

C 87

D 36

F 22

Answers to multiple-choice questions

		Form A		Form B		Form C		Form D
1.		A		C		B		D
2.		B		D		C		C
3.		A		C		C		D
4.		D		B		A		C
5.		D		B		C		B
6.		A		B		A		C
7.		B		A		D		A
8.		B		C		B		C

Answers to free-form questions

The asteroid
a) F(r) = - k r, where k = (4 pi/3) G rho m;
b) F = ma, so we get the differential equation m d²r/dt² = - k r, which has a solution of the form r = r_o cos (omega t + phi), which is S.H.M.;
c) T = 2 pi [3/(4 pi G rho)]^1/2 and t = T/2 = 1.00 h (Forms A,C) or 0.92 h (Forms B,D).

Arnold and the balloons
a) F_net = (rho_A - rho_He) g = 1.089 N;
b) N = mg/F_net = 99 (Form A) or 86 (Form C).

The blimps and the truck
a) F_net = (rho_A - rho_He) g - m_eg = 2.93 x 10⁵ N;
b) N = mg/F_net = 3 (Form B) or 4 (Form D).

Last modified 28 April, 2000. © Gregory C. Sloan.