question_answer

A block of mass 60 kg just slides over a horizontal distance of 0.9 m. If the coefficient of friction between their surfaces is 0.15, then work done against friction will be:

A)  79-4 J                                   

B)  97.54 J

C)  105.25 J                              

D)  none of these

Correct Answer: A

Solution :

                 The free body diagram of the block is as shown. Work done = force \[\times \] displacement Here, \[F=\mu R\] where,   R = Mg \[\therefore \]           \[W=\mu \,Mgs\] \[=0.15\times 60\times 9.8\times 0.9=79.4\,\,\text{J}\]