Amplitude of a mass joined to a spring in the presence of an E-field

[Shivang kohlii]

Homework Statement

A block of mass m having charge q placed on smooth horizontal table and is connected to a wall thorough an unstretched spring of constant k . A horizontal electric field E parallel to spring is switched on. Find the ampliture of the shm by the block.

Homework Equations

kx= qe
U of spring= 1/2kx[2][/SUP]

The Attempt at a Solution

Using conservation of energy and work done by field ,F = qEx
1/2kx^2 = qEx
X (amplitude ) = 2qE/x
But ans isn't this..
In answer directly the forces have been equated
qE = kx
.. I don't understand why has this equation been used to calculate amplitude when conservation of energy is used to calculate the maximum displacement of a body attached to spring when moved from equilibrium position in ?

 

[BvU]

Your problem statement is very incomplete. Could you copy the exact wording ? The way it is formulated now the right answer could as well be the amplitude of the electric field: E !

Your conservation of energy equation is incomplete and F = qEx looks misleading.

 

[Shivang kohlii]

Your problem statement is very incomplete. Could you copy the exact wording ? The way it is formulated now the right answer could as well be the amplitude of the electric field: E !

Your conservation of energy equation is incomplete and F = qEx looks misleading.

I don't understand how to write the conservation of energy equation for this case

 

[BvU]

Your problem statement is very incomplete. Could you copy the exact wording ? The way it is formulated now the right answer could as well be the amplitude of the electric field: E !

It is standard to minimize effort: if something is asked and something else is commented, you ignore the request and comment on the comment.
I realize you have difficulty with this exercise and I am trying to help.
Start with a clear problem description.
If you think you need energies, you should list some energy equations as well.

Is it clear to you what the situation is ? Do you have enough information ?
What is actually happening when E is switched on and what is asked of you (in particular: the amplitude of what?) ? Did you make a sketch ?

 

[PKM]

In answer directly the forces have been equated
qE = kx
.. I don't understand why has this equation been used to calculate amplitude when conservation of energy is used to calculate the maximum displacement of a body attached to spring when moved from equilibrium position in ?

The problem has been correctly solved by equating $qE=kx$.
This eqn applies only when the body is at the extreme positions, as then it has no acceleration $(a)$ there.
In all other positions in between, the eqn of motion is $qE\pm ma=kx$.

 

[BvU]

What does Shivang have to say ?