question_answer

A block of mass 771 having charge q, strings by a spring of spring constant K in a verticle electrostatic field E. The string extension in equiliberium will be:

A)  \[\frac{mg}{K}\]               

B)  \[\frac{qE}{K}\]

C)  \[\frac{mg+qE}{K}\]

D)  \[\frac{mg-qE}{K}\]

Correct Answer: D

Solution :

From the free body diagram as shown below \[qE+K{{K}_{O}}=mg\] \[\therefore \] \[{{X}_{O}}=\frac{mg-qE}{K}\]