question_answer

A block weighs W is held against a vertical wall by applying a horizontal force F. The minimum value of F needed to hold the block is                          [MP PMT 1993]

A)                         Less than W            

B)                           Equal to W            

C)                         Greater than W            

D)                         Data is insufficient

Correct Answer: C

Solution :

                            Here applied horizontal force F acts as normal reaction. For holding the block Force of friction = Weight of block \[f=W\]Þ \[\mu \,R=W\]Þ\[\mu \,F=W\] Þ \[F=\frac{W}{\mu }\]             As \[\mu <1\] \[\therefore \ \ \ F>W\]