Q. A wooden block performs SHM on a frictionless surface with
frequency . The block carries a charge on its surface. If now
a uniform electric field is switched-on as shown, then the
of the block will be Physics Question Image

 4852  181 IIT JEEIIT JEE 2011Oscillations Report Error

Solution:

Frequency or time period of SHM depends on variable forces.
It does not depend on constant external force. Constant external
force can only change the mean position. For example, in the
given question mean position is at natural length of spring in the
absence of electric field. Whereas in the presence of electric
field mean position will be obtained after a compression of .
Where is given by

Correct answer is (a).