3E. A PH-211 student pushes horizontally his physics book against the wall. The

Question

3E. A PH-211 student pushes horizontally his physics book against the wall. The static and kinetic friction coefficients between the book and the wall are u 0.5 and puk 0.4, respectively. The mass of the book is m-lKg. (5 points) If the horizontal force he applies is F- 30 N, what is the magnitude of the friction force acting on the book? CIRCLE YOUR ANSWER a) 9.8 N b) 15 N i) c) 12 N d) 30 N e) NA il) (5 points) If the horizontal force he appies is Fa- 10 N, what is the magnitude of the friction force acting on the book? CIRCLE YOUR ANSWER a)5N b) 19.6 N c) 9.8 N d) 4 N e) NA

Explanation / Answer

Friction force is equal to applied force upto the limiting friction which is equal to static friction times normal reaction here normal reaction is equal to mg = 1×9.8 =9.8 N

Therefore maximum friction force is 9.8×0.5 = 4.9 N

Hence

i) friction force = kinetic friction = 0.4×9.8 = 3.92 N

Hence answer is NA option e)

ii) friction force is equal to kinetic friction i.e. 0.4×9.8 = 3.8 N

Hence answer is NA option e)

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