- #1

k77i

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## Homework Statement

With a block of mass m, the frequency of a block-spring system is 1.5Hz. When 80g is added, the frequency drops to 0.9Hz. Find m and the spring constant k.

## Homework Equations

T=1/f

w=2pi/T

so w= 2pi*f

w^2=k/m

so k=mw^2

T=2pi*sqrt(m/k)

## The Attempt at a Solution

The problem seems simple enough. I just have to set up 2 equations to solve one unknown and then find the other right?

So first i found the w for when the mass= m and f= 1.5Hz (i called this w) and the w for when mass= m+0.08 and f= 0.9Hz (W).

Using the formula w= 2pi*f, i found 9.42 for w and 5.65 for W.

Then I set up the 2 equations:

k = mw^2 = 88.8m

and

k = (m+0.08)W^2 = 31.9m + 2.55

After i did equation 1 = equation 2, so:

88.8m = 31.9m + 2.55 and this gave me m=22.3

But the correct answer for m is supposed to be 0.045 kg. Can somebody let me know what I'm doing wrong please?

The correct value for k is supposed to be 3.99N/m