question_answer

A block of mass 0.1 kg is held against a wall by applying a horizontal force of 5 N on the block. If the coefficient of friction between the block and the wall is 0.5, the magnitude of the frictional force acting on the block is               [IIT 1994]

A)                 2.5 N                     

B)                    0.98 N                

C)                 4.9 N                     

D)                 0.49 N

Correct Answer: B

Solution :

                    Limiting friction \[{{F}_{l}}={{\mu }_{s}}R=0.5\times (5)=2.5\ N\] Since downward force is less than limiting friction therefore block is at rest so the static force of friction will work on it. \[{{F}_{s}}\]= downward force = Weigh\[=0.1\times 9.8=0.98\]N