Solve Spring Frequency Homework: .88kg to .4kg

[jdeakons]

Homework Statement

A mass of .88 kg when fastened to the lower end of a light-weight spring and set vibrating up and down is found to have a frequency of 1.8 Hz. Calculate the new frequency of vibration when the mass is decreased to .4 kg.

Homework Equations

P = 2 \pi \sqrt{m/k}

The Attempt at a Solution

Using K = (m 4 \pi^2 ) / P^2, my answer for K comes out to 112.56.

But, using \sqrt{k} = (\sqrt{m} 2 \pi )/ P, I get 3.2572. But how can that be? The equations are the same, aren't they? Where am I making the mistake?

Thanks.

 

[Snazzy]

2\pi f=\sqrt{\frac{k}{m}}