A) 30 N
B) 40 N
C) 60 N
D) 120 N
Correct Answer: C
Solution :
When the tendency of motion in the block is in upward direction, the force of friction acts in downward direction. So, the net force acting on the block down the plane when it is just about to move up the plane is force of friction plus force of gravity. \[\therefore \] \[{{F}_{\min }}=mg\sin \theta +\mu mg\cos \theta \] Since the inclination is equal to the angle of repose, force of friction is equal to force of gravity. Thus net force acting down the plane in the limiting position \[=2mg\sin \theta \] \[=2\times 5\times 10\times \frac{3}{5}=60\,\,N\]
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