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# Engineering Mechanics - Friction

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### Exercise

• General Questions
"I never see what has been done; I only see what remains to be done."
- Marie Curie
1.

The boy at D has a mass of 50 kg, a center of mass at G, and stands on a plank at the position shown. The plank is pin-supported at A and rests on a post at B. Neglecting the weight of the plank and post, determine the magnitude of force P his friend (?) at E must exert in order to pull out the post. Take B = 0.3 and C = 0.8.

 A. P = 360 N B. P = 264 N C. P = 229 N D. P = 293 N

2.

A uniform beam has a mass of 18 kg and rests on two surfaces at points A and B. Determine the maximum distance x to which the girl can slowly walk up the beam before it begins to slip. The girl has a mass of 50 kg and walks up the beam with a constant velocity.

 A. x = 0.678 m B. x = 0.508 m C. x = 1.005 m D. x = 0.712 m

3.

Determine the minimum force F needed to push the two 75-kg cylinders up the incline. The force acts parallel to the plane and the coefficients of friction at the contacting surfaces are A = 0.3, B = 0.25, C = 0.4. Each cylinder has a radius of 150 mm.

 A. F = 919 N B. F = 735 N C. F = 1.051 kN D. F = 981 N

4.

The refrigerator has a weight of 200 lb and a center of gravity at G. Determine the force P required to move it. Will the refrigerator tip or slip? Take = 0.4.

 A. P = 75 lb Slips B. P = 80 lb Tips C. P = 80 lb Slips D. P = 75 lb Tips

5.

A 17-kg ladder has a center of mass at G. If the coefficients of friction at A and B are A = 0.3 and B = 0.2, respectively, determine the smallest horizontal force that the man must exert of the ladder at point C in order to push the ladder forward.

 A. F = 120.2 N B. F = 288 N C. F = 166.8 N D. F = 204 N