Physics 163

Unit 2: Newton's Laws of Motion

Problem Set B

Problem #7:

Unbeknownst to most students, every time the school floors are waxed, the physics teachers get together to have a barrel of phun doing friction experiments in their socks (uhm - they have clothes on, its just that they don't have any shoes on their feet). On one occasion, Mr. Lewis applied a horizontal force to accelerate Mr. Smith (mass of 80 kg) rightward at a rate of 2.45 m/s/s. If the coefficient of friction between Mr. Smith's socks and the freshly waxed floors is .2, then with what force (in Newtons) must Mr. Lewis be pushing?

• Read the problem carefully and diagram the physical situation (free-body diagram)
• Identify known and unknown information in an organized manner (list on diagram)
• Take the time to plot out a strategy prior to beginning the solution (see graphic below)
• Identify an appropriate formula to use
• Perform step-by-step algebraic manipulations

General information about Set B concepts and principles can be found on the Set B Overview page.

The task of constructing a free-body diagram for a physical situation is discussed in detail at The Physics Classroom.

The task of determining an individual force value if given mass and acceleration information is discussed in detail at The Physics Classroom.

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