# Homework Help: Question on oscillations spring balance and fish

1. Jan 30, 2010

### squintyeyes

The scale of a spring balance reading from zero to 180 N is 7.00 cm long. A fish suspended from the balance is observed to oscillate vertically at 2.50 Hz. What is the mass of the fish? Neglect the mass of the spring.
________ kg

Attempt
k =(180-0)/(7-0) = 25.714 N/m

frequency = (m/k)^(1/2)
2.5 = (m/25.714)^(1/2)
6.25 = m/25.714
m = 160.714 kg

I am pretty certain this is wrong.

2. Jan 30, 2010

### cepheid

Staff Emeritus
I think there are two problems. The first is that the equation is actually:

$$\omega = \sqrt{\frac{k}{m}}$$ ​

and you have the reciprocal of that. The second problem is that omega is not quite the same thing as the frequency of oscillation.

3. Jan 31, 2010

### squintyeyes

yeah but what is the spring constant, K. I sort of need that to solve the problem.