Problem 513 | Friction

Problem 513
In Fig. P-512, the homogeneous block weighs 300 kg and the coefficient of friction is 0.45. If h = 50 cm, determine the force P to cause motion to impend.
 

Tall block on an inclined plane

 

Solution 513

 

Comments

i thought the motion is to impend. why is the force of friction in the same direction as the force P? w

There are two possible answers to this question, depending on which direction you impend the motion. In the absence of force P and for P < 72 kg, motion will surely occur. The P = 72 kg is just enough for the motion to impend downward. This is the solution presented in this page. You may solve the larger value of P; the P that will cause the motion to impend upward. The problem with the larger P however, is that the impending motion is no longer sliding but a rotating motion. If you push the block upward hard enough to overcome the friction, the block will first rotate (or tip over) rather than translate.

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