20140721

Collision type flowchart

"Collision type flowchart"
http://flic.kr/p/o8oHFG
Originally uploaded by Waifer X

Flowchart by Cuesta College Physical Sciences Division instructor Dr. Patrick M. Len.

20140705

Significant figures "flowchart of pain"

"Significant Figures Flowchart of Pain"
http://flic.kr/p/ofhtvx
Originally uploaded by Waifer X

Flowchart by Cuesta College Physical Sciences Division instructor Dr. Patrick M. Len.

20140702

Physics quiz question: units of (mass-specific) heat capacity

Physics 205A Quiz 1, spring semester 2009
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Comprehensive Problem 1.72

The heat Q (measured in units of kg·m2/s2) extracted from an object of mass m that experiences a temperature decrease ∆T (measured in units of K) can be expressed as:

Q = m·c·∆T.

The units for the heat capacity c are:
(A) kg·m2· s–2.
(B) kg-1·m-2·s2.
(C) K·m-2·s2.
(D) K-1·m2·s-2.

Correct answer (highlight to unhide): (D)

From the given expression, the units of these quantities are:

(kg·m2/s2) = (kg)·(units of c)·K,

The units of kg cancel on both sides, and dividing both sides by K gives:

m2/(K·s2) = (units of c).

Response (C) is the inverse of response (D). Responses (A) and (B) are inverses of each other, notably with units of kg instead of units of K.

Student responses
Sections 30880, 30881
(A) : 8 students
(B) : 4 students
(C) : 4 students
(D) : 34 students

"Difficulty level": 68%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.77

Physics quiz question: Newton's form of Kepler's third law

Physics 205A Quiz 1, fall semester 2009
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 1.37

An equation for the period T (measured in units of s) of a planet is given by the expression:

T2 = (4π2·R3)/(G·M).

The orbital radius R is measured in units of m, mass of the sun M is measured in units of kg, and G is a parameter with dimensions. The units for the universal gravitational constant G are:
(A) kg·m3·s-2.
(B) kg·m-3·s2.
(C) kg-1·m-3·s2.
(D) kg-1·m3·s-2.

Correct answer (highlight to unhide): (D)

Solving for G:

G = (4π2·R3)/(T2·M),

such that its units are:

m3/(s2·kg) = m3·s-2·kg-1.

Student responses
Sections 70854, 70855
(A) : 4 students
(B) : 5 students
(C) : 3 students
(D) : 43 students

Success level: 78%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.65

Student responses
Section 72177
(A) : 0 students
(B) : 4 students
(C) : 1 student
(D) : 10 students

Success level: 66%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.29

Physics quiz question: Planck length expression

Physics 5A (currently Physics 205A) Quiz 1, fall semester 2007
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Comprehensive Problem 1.73

Three of the fundamental constants of physics are:

      The universal gravitational constant, G = 6.7×10-11 m3·kg-1·s-2.
      The speed of light, c = 3.0×108 m·s–1.
      Planck's constant, h = 6.6×10-34 m2·kg·s-1.

What is the combination of these three constants that has the dimensions of length? This length is called the Planck length and represents the scale at which quantum mechanics becomes important.
(A) G(3/2) × c(1/2) × h(-1/2).
(B) G(1/2) × c(3/2) × h(-1/2).
(C) G(3/2) × c(-1/2) × h(1/2).
(D) G(1/2) × c(-3/2) × h(1/2).

Correct answer (highlight to unhide): (D)

The Planck length is in units of m, thus all units of kg and s must cancel out. The speed of light c has units of m/s, and notably does not have units of kg. The universal gravitational constant G has units of kg-1, and h has units of kg, so they must be raised to the same power, in order for the kg units to cancel out. This eliminates choices (A), (B), and (C) as G and h are not raised to the same power, and thus the only remaining choice (D) (where G and h have are raised to the same power) must be the correct answer.

Student responses
Sections 0906, 0907
(A) : 5 students
(B) : 14 students
(C) : 13 students
(D) : 9 students

Success level: 24%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.19

Physics quiz question: solar intensity conversion

Physics 5A (currently Physics 205A) Quiz 1, spring semester 2008
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 1.16

The intensity of the sun's radiation that reaches Earth's atmosphere is 1.4 kW/m2 (kW = kilowatt; W = watt). This intensity, in units of W/mm2, is:
(A) 1.4×10-6 W/mm2.
(B) 1.4×10-3 W/mm2.
(C) 1.4 W/mm2.
(D) 1.4×103 W/mm2.

Correct answer (highlight to unhide): (B)

Relevant conversion factors are 1 kW = 1,000 W and 1 m = 1,000 mm. Then setting up conversion factors such that unwanted units cancel (kW, m) while desired units remain (W, mm):

1.4 kW/m2 = (1.4 kW/m2)·(1,000 W/1 kW)·(1 m/1,000 mm)·(1 m/1,000 mm) = 1.4×10-3 W/mm2.

Student responses
Sections 4987, 4988
(A) : 7 students
(B) : 6 students
(C) : 18 students
(D) : 8 students

Success level: 31%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.37