崔屁屁 asked in 科學其他:科學 · 1 decade ago

A horizontal force of 12N push

A horizontal force of 12N pushes a 0.5-kg book against a vertical wall. The book is initially at rest. If the coefficients of friction are ms = 0.6 and mk = 0.8 which of the following is true?

A. The magnitude of the frictional force is 4.9N

B. The magnitude of the frictional force is 7.2N

C. The normal force is 4.9N

D. The book will start moving and accelerate

E. If started moving downward, the book will decelerate

1 Answer

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  • 1 decade ago
    Favorite Answer

    By Newton's third law, the normal reaction force from the wall is 12 N.

    Thus, maximum possible static friction from the wall on the book = 12 x 0.6 = 7.2 N

    But since the book's weight is 0.5 x 9.8 = 4.9 N, the frictional force is 4.9 N in order to keep the book stationary.

    Ans = A

    Source(s): Myself
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