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**1. The problem statement, all variables and given/known data**

An object of mass M = 4 kg slides from rest a distance d = 4 m down a frictionless inclined plane where it encounters a spring. It compresses the spring a distance D = 1 m before stopping. The inclined plane makes an angle q = 20° with the horizontal.

**2. Relevant equations**

When the block just touches the spring, how much gravitational potential energy has it lost?

U=53.7 J

After the mass has fully compressed the spring, what is its total loss of gravitational potential energy?

U=67.1 J

What is the value of the spring constant?

k=??

**3. The attempt at a solution**

U=Ui-Uf

U=53.7-67.1=-13.4

U=(1/2)kx^2

k=2U/x^2

k=2(-13.4)/(5)^2

k=1.07????

the answer is wrong. am i suppose to use the conservation of mechanical energy? because i am lost.