JEE Main & Advanced
Sample Paper
JEE Main Sample Paper-47
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. \[\Rightarrow \] \[x=(d-f),\,\,\,y=-f\theta \]