Category Archives: High School

Items appropriate for use in a high school physics course.

A2L Item 169

Goal: Link acceleration to the slope of a velocity/time graph

Source: CT151.2-6

An
object’s motion is described by the graph above. The instantaneous
acceleration at t=10 sec is most nearly…

  1. 0 m/s2
  2. -2 m/s2
  3. 3 m/s2
  4. -4 m/s2
  5. 5 m/s2
  6. Other

Commentary:

Answer

(1) Useful follow-up questions include; when does the object have
positive acceleration, when negative acceleration; does the object ever
stop?; when is it farthest from the origin?

A2L Item 163

Goal: Problem solving and developing strategic knowledge

Source: UMPERG-ctqpe101

You are given this problem:

A
block sits on a frictionless incline. Given the angle of incline, the
distance along incline, and the mass of block, find the acceleration
after traveling a distance d.

What principle would you use to solve the problem MOST EFFICIENTLY?

  1. Kinematics only
  2. F = ma or Newton’s laws
  3. Work-Energy theorem
  4. Impulse-Momentum theorem
  5. Angular Impulse-Ang. Momentum
  6. More than one of the above
  7. Not enough information given

Commentary:

Answer

(2) The 2nd law is needed to find the acceleration. Students who
answer that only kinematics is needed are relying on memory.

A2L Item 161

Goal: Problem solving with kinematics

Source: CT151.2-4

Ann is running with a constant speed of 3 m/s on a straight track. Deb
is also running with constant speed but is initially 10 m behind Ann. If
Deb catches up to Ann after Deb has traveled 55 m, how fast is Deb
running?

  1. 3.2 m/s
  2. 3.55 m/s
  3. 3.75 m/s
  4. 4.15 m/s
  5. More than 4.2 m/s
  6. none of the above
  7. cannot be determined

Commentary:

Answer

(6) The correct speed is 3.67 m/s. Students indicating #2 or #3
are likely making an arithmetic error. Have students graph the position
vs. time graphs for each runner.

A2L Item 160

Goal: Developing a strategic approach to problem solving

Source: CT151.2S02-44 spinoff

A cart
of mass 2m collides and sticks to a cart of mass m that is initially at
rest. The combination of the two then moves together. Which of the
following principles would be the most efficient way to find the final
speed of the combination?

  1. The Work/Energy Theorem
  2. Newton’s Laws and the basic equations of motion
  3. Conservation of Energy
  4. Conservation of Momentum
  5. Conservation of Angular Momentum
  6. A different principle entirely.
  7. Two (or more) of them would be equally efficient.
  8. Need more information.

Commentary:

Answer

(4) It is valuable to always associate conservation of momentum
with the third law. In addition, it is worthwhile to distinguish totally
inelastic collisions from typical inelastic collisions.

A2L Item 159

Goal: Explore momentum concepts

Source: CT151.2S02-44

A cart
of mass 2m collides and sticks to a cart of mass m that is initially at
rest. What is the speed of the combination after the collision?

  1. v
  2. 2v/3
  3. v/3
  4. 0
  5. None of the above.
  6. Cannot be determined.

Commentary:

Answer

(2) This question is useful for probing pre-existing ideas about
momentum, and also for distinguishing momentum ideas from kinetic
energy. It should be used just after, or even before, covering momentum
concepts.

Usually students starting momentum already have had some energy, and
kinetic energy in particular. If appropriate, they can be asked if
energy is lost in the collision. Is more or less energy lost if the
carts do not stick together?

A2L Item 158

Goal: Hone the concept of displacement

Source: CT151.2-2

Bekki walks 3 m to the right, 4 m to the left, 5 m to the right, and 2 m
to the left. What is her displacement?

  1. 0 m
  2. 2 m
  3. 2 m (to the right)
  4. 2 m (to the left)
  5. 14 m (to the right)
  6. 8 m to the right and 6 m to the left
  7. impossible to determine
  8. none of the above

Commentary:

Answer

(3) Students need to distinguish between distance and
displacement. Questions such as this are good introductions to vectors.

A2L Item 154

Goal: Distinguish distance traveled from displacement

Source: CT151.2-1

Andy has the following series of displacements: 3 m to the right; 4 m to
the left; 5 m to the right; and 2 m to the left. What is his distance
traveled?

  1. 0
  2. 2 m
  3. 2 m (to the right)
  4. 2 m (to the left)
  5. 14 m (to the right)
  6. 8 m (to the right)
  7. Impossible to determine
  8. None of the above

Commentary:

Answer

(8) Students just learning about vectors and displacements are
inclined to over specify quantities. Before they knew anything about
vectors they used distance as a scalar but can become confused and give
it the direction of the total displacement.

A2L Item 153

Goal: Hone the concept of impulse

Source: UMPERG-ctqpe80

A MOVING car collides with a STATIONARY truck. Which of the following
statements is true about the magnitudes of the impulse on each due to
the other?

  1. The impulse on the car is larger than the impulse on the truck.
  2. The impulse on the truck is larger than the impulse on the car.
  3. The magnitudes of the two impulses are equal.
  4. Answer depends upon circumstances of the collision.

Commentary:

Answer

(3) The 3rd law requires that the impulses be equal. Even
students who understand the 3rd law have difficulty realizing that the
magnitude of the impulse on two interacting bodies is the same. Many
students, however, do not understand impulse enough to recognize the
association. Others do not read the problem carefully enough and answer
with regard to ALL the forces, not just the one due to the other
vehicle.

A2L Item 151

Goal: Reason with kinematics

Source: UMPERG-ctqpe75

Two identical steel balls are released from rest from the same height,
and travel along tracks as shown and labeled below.

Which ball reaches the end of its track first?

  1. ball on track A
  2. ball on track B
  3. they reach the end at the same time
  4. not enough information

Commentary:

Answer

(2) The ball on track B accelerates down the second slope. A
component of this acceleration is in the x-direction. This means that
the x component of ball B’s velocity is never smaller than that of ball
A. Since the tracks have the same x-dimension, ball B gets there first.

A large majority of students choose answer C incorrectly thinking that
since the balls return to the same height, they have the same speed and,
therefore, arrive at the same time.

A2L Item 152

Goal: Reason with kinematics

Source: UMPERG-ctqpe76

Two identical steel balls are released from rest from the same height,
and travel along tracks as shown and labeled below.

Which reaches the end of its track first?

  1. Ball on track A
  2. Ball on track B
  3. They reach the end at the same time
  4. Not enough information

Commentary:

Answer

(2) The ball on track B accelerates down the second slope. A component
of this acceleration is in the x-direction. This means that the x
component of ball B’s velocity is never smaller than that of ball A.
Since the tracks have the same x-dimension, ball B gets there first.

A large majority of students choose answer C incorrectly thinking that
since the balls return to the same height, they have the same speed and,
therefore, arrive at the same time.