Question

7. A 5kg block is resting on an inclined plane at an angle of 25º. What is the normal force on the block? 250 8. If the same block is just barely being held in place by friction, what is the coefficient of static friction? (Total 20 pts; Free Body Diagram: 10pts; equation setup: 6pts; correct answer, with proof: 4pts.)

Answer 1

Since the block is at rest, the acceleration along the incline and perpendicular to incline will be zero. Write equations of motion along the incline and perpendicular to incline with zero acceleration to find the required value of normal force and coefficient of static friction as shown below

mgsinoti Ingcoso so 70 Acceleration along perpendicular to incline is zero, so No - mg coso = ma 3) No - mg cose = 0 =) No = ingcose = (sky)(9.8m|52) coses' = 144.4 N = normal - force 8) {f- fiction Acceleration parallel to incline is zeso. So, egy of motion along incline is mgsine - f = 0 - f = mgsino but f = US No = is mgcoso so, mgsino = is mg cose = us = tano = tanzs° = 10.47

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