# Elastic collision, I think?

#### geauxKTM

Elastic collision, I think???

1. The problem statement, all variables and given/known data50kg boulder slides down a 5m high, 20m long hill against friction force 40N. At the top the boulder is moving at 2m/s. At the base of hill the boulder slides on a horizontal frictionless surface for a short distance and then collides with a tree having spring constant 5000N/m. A. Find the kinetic energy at the bottom of the incline. B. find distance the spring(tree) is compressed or bent when the boulder stops

2. Relevant equations Ff=40N m=50 V0=2 Im lost. For B f=kx right?

3. The attempt at a solution No attempt and I have 3 of the smarter students sitting with me so please help. I seem to always receive feedback too late and I realize this is a weak attempt but I do have at least 4 more to post with a better understanding

#### rock.freak667

Homework Helper
Re: Elastic collision, I think???

Use conservation of energy. What is the total energy at the top? What is the work done by friction? When you get these two, you can get the kinetic energy at the bottom.

#### geauxKTM

Re: Elastic collision, I think???

Use conservation of energy. What is the total energy at the top? What is the work done by friction? When you get these two, you can get the kinetic energy at the bottom.
Thank you very much, is this right?. A.Ui+W=Kf (50(9.8)5)+(40*20)=3250J
B. 3250=500x^2

#### rock.freak667

Homework Helper
Re: Elastic collision, I think???

Your equation should be mgh=1/2 mv2+Ffrictiond. Not sure which quantities were represented by your symbols.

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