Three identical boxes sit on a concrete floor. Each box weighs 160 N. Each has a

Question

Three identical boxes sit on a concrete floor. Each box weighs 160 N. Each has a coefficient of static friction with the floor of 0.66 and a coefficient of dynamic friction of 0.58. Geoff pushes on the first box with a horizontal force of 50 N. Mary pushes on the second box with a horizontal force of 100 N. Jim pushes on the third box with a horizontal force of 150 N. a. Do any of the boxes move? If so, which one(s)? Explain the rational for your answer(s). Include a general free body diagram that can be used to analyze all three boxes. b. Calculate the actual frictional force that is elicited between the ground and the box in each case. In other words, for those boxes that move, compute the dynamic friction that resists the sliding. For those boxes that do not move, compute the static friction that resists the applied force. (Note: Be careful! The frictional force is not necessarily maximum in each case.)

Explanation / Answer

Ffs (maximum static frictional force) = us m g = us W Ffs = 160 * .66 = 106 N a) only the third box will move b) actual frictional force: first box = 50 N second box = 100 N For the third box Ffk = uk W = .58 * 160 = 93 N So 93 N is the frictional force on the third box.

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