Charged mass connected to spring, swung in circle in mag. field

[clubguppy]

Homework Statement

A spring with an unstretched length of 20 cm and a force constant of 100 N/m is attached to a 2-kg mass with a charge of 3.0 C. The mass is swung in a circle in a zero gravity environment, so that the spring is perfectly horizontal and is parallel to the radius of the circle, as shown at right. A vertical 1.5-T magnetic field permeates the entire region.


If the mass is moving at 5 m/s, what is the maximum radius of its motion?

Homework Equations

Centripetal Force: F= \frac{mv^{2}}{r}
Hooke's Law: F=kx where k is the spring constant and x is elongation (how long the string is stretched)
Magnetic Force: F = qvBsin \theta

The Attempt at a Solution

I tried qvBsin(90 degrees) = qvB =F= \frac{mv^{2}}{r} + kr
I assumed the force on the spring itself is the tenion (the constant * how long it stretched)

I'm not sure if I did it correctly...please help.

 

[mukundpa]

What is x in F = kx ?

 

[clubguppy]

Reply

Homework Statement

A spring with an unstretched length of 20 cm and a force constant of 100 N/m is attached to a 2-kg mass with a charge of 3.0 C. The mass is swung in a circle in a zero gravity environment, so that the spring is perfectly horizontal and is parallel to the radius of the circle, as shown at right. A vertical 1.5-T magnetic field permeates the entire region.


If the mass is moving at 5 m/s, what is the maximum radius of its motion?

Homework Equations

Centripetal Force: F= \frac{mv^{2}}{r}
Hooke's Law: F=kx where k is the spring constant and x is elongation (how long the string is stretched)
Magnetic Force: F = qvBsin \theta

The Attempt at a Solution

I tried qvBsin(90 degrees) = qvB =F= \frac{mv^{2}}{r} + kr
I assumed the force on the spring itself is the tenion (the constant * how long it stretched)

I'm not sure if I did it correctly...please help.

I have updated the information in the question.

 

[mukundpa]

is the elongation is equal to radius of the circular path?

 

[clubguppy]

response

is the elongation is equal to radius of the circular path?

Yes, that is what I assumed. But, I can't get the radius in real number. What did I do wrong? Do you have suggestions for what I should do?

Should I change something about qvB =F= \frac{mv^{2}}{r} + kr or do something different?