- #1

idir93

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**Can the spring constant "k" be negative ?**

Hi,

I found a difficulty when solving this problem from my textbook :

In the arrangement of Figure 7-11 (which is basically a standard block attached to spring resting horizontally), we gradually pull the block from x = 0 to x = +3.0 cm, where it is stationary. Figure 7-36 gives the work that our force does on the block. We then pull the block out to x = +5.0 cm and release it from rest. How much work does the spring do on the block when the block moves from xi = +5.0 cm to (a) x = +4.0 cm, (b) x = –2.0 cm, and (c) x = –5.0 cm?

So I found the spring constant k:

W = -0.5kx2

0.9 = -0.5k(0.03)2

k = -2000 N/m ? of course it's wrong (the correct answer is 2000 N/m) but i couldn't find my mistake.

Please help me :)