Recitation Worksheet H Solutions

Recitation Worksheet H Solutions - Worksheet H: Friction...

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Worksheet H: Friction and dynamics of circular motion. 1 . A box of mass m = 1.2 kg sits on a plane whose inclination θ can be changed. The coefficients of friction between the box and the plane are μ s = 0.40 and μ k = 0.20. a. Draw the free body diagram of the box. b. What is the magnitude of the friction force when the angle is 5º? (The box does not move at this angle, as you will prove in part c) Newton’s second law along the incline: () 2 sin 0 sin 1.2 kg 9.8 m/s sin5 1.0 N s s mg f fm g −= = = c. Find the critical angle c for which the box starts to slide. This happens when static friction achieves its maximum value. max max sin 0 s ss mg f with f N µ = Newton’s 2 nd law in the direction perpendicular to the incline: cos 0 cos Nm g g = Thus, sin 0 sin cos 0 tan s mg N mg mg µθ = = 1 tan s θµ = 1 tan (0.40) 22 = m mg N f s
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(Worksheet H) d. What is the acceleration of the box at this angle? Right when the box begins sliding, the friction becomes kinetic. Newtons’ second law then reads: () () () 22 sin with cos cos 0 cos sin
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This homework help was uploaded on 03/27/2008 for the course PHYS 221 taught by Professor Herrera-siklody during the Fall '08 term at Iowa State.

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Recitation Worksheet H Solutions - Worksheet H: Friction...

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