# Homework Help: Spring - which one is correct?

1. Dec 28, 2009

### JoanF

1. The problem statement, all variables and given/known data
mass of the body=m

Horizontally, the spring is deflected from its equilibrium position and then released, oscillated with a frequency f. Then, the same spring and the same body are suspended vertically, as in figure.

Which one is correct?

A) The frequency of movement of the spring, when the body is suspended vertically, doubled.

B) The frequency of movement of the spring, when the body is suspended vertically, reduced to half.

C) The frequency of movement of the spring, when the body is suspended vertically, remains the same.

D) The frequency of movement of the spring, when the body is suspended vertically, is not related to the period of the movement, when the spring oscillates horizontally.

2. Relevant equations

3. The attempt at a solution

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

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2. Dec 28, 2009

### Staff: Mentor

Re: Spring

Describe how you came to that conclusion.

3. Dec 28, 2009

### JoanF

Re: Spring

I think is C) because the frequency is a characteristic of the oscillator.

I think that D) is also correct because we change the position of oscillator and in the second case there are 2 forces: grav force and elastic force, in the first case there is only elastic force.

4. Dec 28, 2009

### Staff: Mentor

Re: Spring

It's true that when suspended vertically there are two forces to consider, but it still turns out that the frequency depends only on the ratio of k/m.

How does period relate to frequency?

5. Dec 28, 2009

### JoanF

Re: Spring

f= 1/T

so is C) ?

6. Dec 28, 2009

### Staff: Mentor

Re: Spring

Right.
Yes, C is correct. D doesn't really make sense, since if the frequency is unchanged the period must also be unchanged.

7. Dec 28, 2009

### JoanF

Re: Spring

so the in spite of in 2nd case there are 2 forces acting, that doesn't change anything, right?

8. Dec 28, 2009

### Staff: Mentor

Re: Spring

What changes is the length of the spring when the system is at its equilibrium point. In the horizontal case, the equilibrium position is when the spring is unstretched; but when vertical, the spring is stretched at equilibrium (by an amount = mg/k).

But that doesn't affect the choice of answer.

9. Dec 28, 2009

### JoanF

Re: Spring

oh ok, now I understand

many thanks, really!