Tag Archives: Work-Energy Theorem

A2L Item 162

Goal: Problem solving and developing strategic knowledge

Source: UMPERG-ctqpe100

You are given this problem:

A
mass m slides down a frictionless track of radius R=0.5m. Relative to
the center of curvature, what is the angular acceleration of the mass as
it reaches the bottom of the track.

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-Angular Momentum
  6. 1 & 2
  7. 1 & 3
  8. 2 & 3
  9. none of the above
  10. not enough information given

Commentary:

Answer

(7) Students often think this problem requires angular momentum
or angular dynamics. Many cue on anything circular. Some students may
answer #10 thinking that the mass is needed.

A2L Item 156

Goal: Developing strategic knowledge

Source: UMPERG-ctqpe85

A mass of 0.5 kg moving along a horizontal frictionless surface
encounters a spring having k = 200 N/m. The mass compresses the spring
by 0.1 meters before reversing its direction. Consider the total time
the mass is in contact with the spring. What is the total impulse
delivered to the mass by the spring?

Which of the following principles or combination of principles
could be used to solve this problem MOST EFFICIENTLY.

  1. Newton’s 2nd law & dynamics
  2. Work-Energy theorem
  3. Impulse-Momentum theorem
  4. 1 and 2
  5. 1 and 3
  6. 2 and 3
  7. Other

Commentary:

Answer

(6) This is a two-principle problem. Again, student response is
not as important as discussing what clues there are for deciding what
principles are needed.