question_answer

Light of frequency \[v\] falls on material of threshold frequency\[{{v}_{\operatorname{o}}}\]. Maximum kinetic energy of emitted electron is proportional to:

A) \[v-{{v}_{o}}\]                         

B) \[v\]      

C) \[\sqrt{v-{{v}_{o}}}\]               

D) \[{{v}_{o}}\]

Correct Answer: A

Solution :

Let 'x' be the number of men required for the block to just start moving up the plane \[\operatorname{xF} = mg sin 45{}^\circ +{{f}_{r}}~~{{f}_{\operatorname{r}}}={{\mu }_{\operatorname{s}}} R \Rightarrow \mu mg cos 45{}^\circ \] \[\operatorname{x}\times 500=mg\left[ \frac{1}{\sqrt{2}}+\frac{1}{2}\times \frac{1}{\sqrt{2}} \right]\] \[500\operatorname{x}=\frac{200\times 10}{\sqrt{2}}\times \frac{3}{2}\] \[\operatorname{x}=5\]