# what is the spring constant of a spring with retractable tip pen that stores 0.008J potential energy when compressed by 1cm.

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This is related to Hooke's law

The energy stored in a spring can be given as;

`E = 1/2xxkxxx^2`

Where

E = stored energy which is 0.008J

k = spring constant

x = amount of compression which is 1cm or 0.01m

`E = 1/2xxkxxx^2`

`0.008 = 1/2xxkxx0.01^2`

`k = 160`

**So the spring constant is 160N/m**

**Sources:**