Author Archives: Automated Transfer Script

A2L Item 125

Goal: Problem solving with dynamics

Source: UMPERG-ctqpe21

Two blocks rest on a frictionless surface. Both blocks move to the right
with acceleration of 2 m/s2. The force on the big block due
to the small block is

  1. 14N to the right
  2. 10N to the left
  3. 8N to the right
  4. 6N to the left
  5. 4N to the right
  6. 2N to the left
  7. none of the above
  8. cannot be determined

Commentary:

Answer

(7) The force on the small block must cause the specified acceleration.
The 3rd law requires that the force on the big block be equal and
opposite. The magnitude is 4N but it is directed to the left.

A2L Item 124

Goal: Link flux and enclosed charge.

Source: 283-410 Flux greatest?

Consider the flux through the following spherical Gaussian surfaces.
Take each charge distribution to be either a point charge or a spherical
shell of charge (uniformly distributed). For which situation is the flux
greatest?

  1. a and c
  2. a, b, and c
  3. b
  4. a
  5. b, c, and e
  6. a, f, and g
  7. b, c, and g
  8. Other

Commentary:

Answer

(2) All these have the same flux. Some students do not read the question
carefully and think the number of ‘+’ signs matter.

A2L Item 123

Goal: Reasoning with electric fields.

Source: UMPERG-A2LEM7

The diagrams show two uniformly charged spheres. The charge on the
right sphere is three times as large as the charge on the left sphere.
Each vector represents the electric field at the center of one sphere
caused by the other sphere. Which choice best represents the
magnitude and direction of the electric field vectors caused by one
sphere at the position of the other sphere?

Commentary:

Answer

(5) The electric field at the sphere with smaller charge is three times
larger than the field at the sphere with larger charge.

A2L Item 122

Goal: Reasoning with Coulomb’s law

Source: UMPERG-A2LEM6

The diagrams show two uniformly charged spheres. The charge on the
right sphere is three times as large as the charge on the left sphere.
The arrows on each charge represent the force on the charge. Which
force diagram best represents the magnitude and direction of the
electric forces on the two spheres?

Commentary:

Answer

(4) By Newton’s third law the forces are equal and opposite.

A2L Item 118

Goal: Hone the vector nature of electric force.

Source: UMPERG-A2LEM2

Two charges, a negative charge Q, and a positive charge q, are
positioned as shown in the diagram. What is the direction of the
electrical force on q due to Q?

Commentary:

Answer

(3) The force is attractive.

A2L Item 115

Goal: Reasoning about temperature.

Source: UMPERG-ctqpe186

Two moles of an ideal gas fill a volume of 10 liters with a pressure of
2.4 atm. The gas is thermally insulated from the surroundings. A
membrane is broken which allows the gas to expand into the new volume
which is 3 times as large as the old volume. The new temperature is …

  1. The same as before.
  2. Lower than before.
  3. Higher than before.
  4. Cannot be determined.

Commentary:

Answer

(1) Students may erroneously apply prior knowledge that gas cools as it
expands. Some will likely think that the answer cannot be determined
without more information.