question_answer

Find frictional force on block 30 kg

A)  20 N                          

B)  30 N

C)  40 N                          

D)  50 N

Correct Answer: B

Solution :

 As given \[m=10\,kg\] FBD for upper block (10 kg) As maximum static friction \[={{\mu }_{s}}N=0.5\,\times 10\times g=50N\] As 60 N is greater than force of static friction (maximum) So, block will slip over the lower one and hence force of kinetic friction \[{{f}_{k}}\] has to be considered in that case. and \[{{f}_{k}}={{b}_{k}}\,\,N=0.3\times 10\times 10=30\,N\]             \[u=\infty \,\,\Rightarrow \,\,v=f\] (from mirror formula) Also,    \[{{h}_{I}}=-f\,\theta \] For plane mirror object distance is d - f. \[\Rightarrow \]            \[x=(d-f),\,\,\,y=-f\theta \]