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A2L Item 139

Meta-Information
Description: 
Indicate which action takes the least work.
Goal: 
Reasoning with work
Level: 
Undergraduate
Keywords: 
Mechanics
Keywords: 
Work
Source: 
UMPERG-ctqpe50

In which case would you do the least amount of work?

  1. You push a box 10 m across a floor.
  2. You pick up the box, walk 10 m and put the box down on the floor.
  3. You pick up the box, walk 10 m and drop the box.
  4. Both 2 and 3
  5. Work done is the same in all cases.
  6. Cannot be determined from info given.
Commentary

Answer

(6) This problem is intended to elicit a vigorous discussion of work. Students have a difficult time reconciling the formal definition of work with the colloquial one. Every one of the answers is defensible depending upon one’s perspective. Lifting a heavy box requires doing work against gravity. Putting it down actually requires that you do the same amount of work. Gravity does no net work, but humans are not conservative systems. Depending upon the surface it may be more advantageous to push the box.