Category Archives: Uncategorized

A2L Item 285

Goal: Unspecified.

Source: Unspecified.

Two blocks with mass m2>m1 sit on a horizontal surface having friction. Both blocks are pulled with a constant speed, but v2 < v1, by a rope under tension. Which tension does the most work moving the block a distance D along the
surface?

  1. T1
  2. T2
  3. Both do the same work.
  4. Cannot be determined.

Commentary:

None provided.

A2L Item 284

Goal: Unspecified.

Source: Unspecified.

Two blocks with mass m2>m1 sit on a horizontal surface having friction. Both blocks are pulled with the same constant speed, v, by a rope under tension. Which tension does the most work moving the block a distance D along the surface?

  1. T1
  2. T2
  3. Both do the same work.
  4. Cannot be determined.

Commentary:

None provided.

A2L Item 282

Goal: Unspecified.

Source: Unspecified.

A string attached to an 8 kg mass is passed over a frictionless pulley and attached to a 2 kg mass as shown. What is the tension in the rope supporting the pulley? (Use g=10 N/kg)

  1. 0 N
  2. 20 N
  3. 40 N
  4. 60 N
  5. 80 N
  6. 100 N
  7. None of above.
  8. Can’t be determined.

Commentary:

None provided.

A2L Item 283

Goal: Unspecified.

Source: Unspecified.

Consider the situations shown. Let m < M. Which spring has the largest spring force?

  1. A
  2. B
  3. C
  4. A & B are equal.
  5. A & C are equal.
  6. B & C are equal.
  7. All are the same.
  8. Not enough information.

Commentary:

None provided.

A2L Item 281

Goal: Unspecified.

Source: Unspecified.

A string attached to an 8 kg mass is passed over a frictionless pulley and attached to a 2 kg mass as shown. What is the normal force on the 8 kg block? (Use g=10 N/kg)

  1. 0 N
  2. 20 N
  3. 40 N
  4. 60 N
  5. 80 N
  6. 100 N
  7. None of above.
  8. Can’t be determined.

Commentary:

None provided.

A2L Item 207

Goal: Hone the conservative nature of the electrostatic field

Source: 283-240 Work moving charge around

Two point charges are fixed on the x-axis. A positive charge from point
P to the origin along the different paths shown in the diagram below.
For which path would you do the most work?

  1. Path A
  2. Path B
  3. Path C
  4. Path D
  5. Cannot be determined
  6. None of the above

Commentary:

Answer

(6) Relating the work done to the change in potential should be
stressed. Once this point is made, a good follow-up question is to ask
how much work would be done if one of the charges on the x-axis was
negative.

A2L Item 198

Goal: Honing the right hand rule

Source: UMPERG-283 Mag Force

In a region of space there is a uniform magnetic field pointing in the
positive z direction. In what direction should a negative charge move
to experience a force in the positive x direction?

  1. In the positive z direction
  2. In the negative z direction
  3. In the positive x direction
  4. In the negative x direction
  5. In the positive y direction
  6. In the negative y direction
  7. It can move in any direction
  8. The force cannot be in the +x direction

Commentary:

Answer

(6) Students will likely forget that the charge is negative.

A2L Item 150

Goal: Link work and potential

Source: 283-465 Interpreting voltage

The potential at two points in space is: V1=200 Volts,
V2=300 Volts. Which of the following statements is true for
moving a point charge, q, from point 1 to 2?

  1. The work done by an external agent to
    move q from point 1 to 2 is positive.
  2. Can’t determine the work
    done because you don’t know the direction of V at the two points.
  3. The work done by the electrical force exerted on q in moving it from
    point 1 to 2 is: W = -q(100 Volts).
  1. A
  2. B
  3. C
  4. A and B
  5. A and C
  6. A, B, and C
  7. None of the above

Commentary:

Answer

(3) is the best response. Statement A is true only if the charge
is positive. The important thing is to see if students correctly
envision the electric field lines as directed from higher potential to
lower.

Any response involving statement B should be discussed thoroughly as it
indicates confusion between fields and potentials.

A2L Item 051

Goal: Reasoning about the vector nature of force.

Source: UMPERG

A rock sits on a hillside. The slope of the hillside is inclined to the
horizontal at approximately 30°.

Which of the forces exerted on the rock is smallest in magnitude?

  1. Friction force due to the ground
  2. Gravitational force due to the Earth
  3. Normal force due to the ground
  4. The Friction, Gravitational and Normal force are equal in magnitude
  5. Cannot be determined
  6. None of the above

Commentary:

Answers

(1). The smallest force is the friction force. The normal force
balances the component of gravity perpendicular to the hillside and the
friction force balance the component of gravity parallel to the
hillside. Since the hillside has a slope of 30°, the tangential
component of gravity is smaller.

Background

Many students fail to perceive that the static situation implies a
relationship between the forces. They may think that one requires
information such as the mass, and coefficient of friction to compute the
forces before the forces can be compared.

Questions to Reveal Student Reasoning

Can you determine the gravitational force? …normal force? …
friction force? Are there any relationships between these forces? If
so, what are they? Why doesn’t the rock slide down the hill?

Suggestions

Draw a free-body diagram.

Set up a demonstration using a block on a plane with adjustable angle.