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 \[qE+K{{K}_{O}}=mg\] \[\therefore \] \[{{X}_{O}}=\frac{mg-qE}{K}\]