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## Homework Statement

In order to compress a spring by 7cm from its natural length, 20J of work has to be done. How much additional work should be performed in order to compress the spring by an additional 7cm?

## Homework Equations

F= -Kx (spring's equation)

W=1/2(Kx)x = [k(x)^2]/2 (Work equation and spring's equation)

## The Attempt at a Solution

20J = [K (7)^2]/2 (Solving for k, but I get the same answer of 20J when substituting k in the work equation)

Although the answer seems to be 20J as you are stretching it an additional 7cm, that answer is wrong. The answer in the back of the book says it is

**60J**.