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

A spring of length 0.80 m rests along a frictionless 30 degree incline. A 2.0 kg mass, at rest against the end of the spring, compresses the spring by 0.10 m.

A) Determine the spring constant k .

B) The mass is pushed down, compressing the spring an additional 0.60 m, and then released. If the incline is 2.0m long, determine how far beyond the rightmost edge of the incline the mass lands.

2. Relevant equations

Fspr = k*x

Wspr = .5*k*x^2

3. The attempt at a solution

For part A, I get two different answers for the spring constant depending on whether I try to use forces or energy. Can somebody explain why one way is correct? Why doesn't forces/energy give the correct answer?

Fspr = Fg parallel to the incline

k*x = m*g*sin(30)

k*.1 = 2*9.8*sin(30)

k = 98 N/m

Wspr = PEg

.5*k*x^2 = m*g*x*sin(30)

.5*k*.1^2 = 2*9.8*.1*sin(30)

k = 196 N/m

Thanks.

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# Homework Help: Spring - Forces or Energy?

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