In: Mechanical Engineering
The 40 lb plank A rests on the 30 lb block B as shown in Figure 5. The coefficient of static friction between the plank and the block is μAB = 0.35 and between the block and the ground is μBD = 0.25. Determine the largest force P that can be applied to the plank without causing motion. Report your answer in lbs but do not enter units. Neglect the thickness of the plank. Consider and show all possibilities of motion.
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1) If the force P exceeds 14 lb, then plank A will move relative to block B because the force P has exceeded the maximum frictional force between plank A and block B ( fA= 14 lb)
2) The force pulling the block B is the frictional force between the plank A and the block B. Even if this frictional force is maximum ( fA=14 lb), it is still less than the maximum frictional force between the block B and the ground (fB= 17.5 lb).Hence, block B will not move at all even if the force P exceeds 14 lb because the pulling force of block B can have only a maximum value of 14 lb, which is less than the maximum frictional force between block B and the ground (17.5 lb)...
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