Day 57: UBFPM Whiteboarding

We are now getting to the challenging problems where students apply the unbalanced-forces particle model to problems involving multiple objects and friction in unexpected ways. Here is one of my favorite problems: The diagram below shows a large cube of mass 25 kg being accelerated across a friction- less level floor by a horizontal force, F. A small cube of mass 4.0 kg is in contact with the front surface of the cube. The coefficient of static friction between the cubes is 0.71. What is the minimum value of such that the small cube will not slide down the large cube’s side? Here is one group’s whiteboard solution: IMG_0741   ##ufpm ##whiteboarding  

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