# Upward velocity of a block on a string

by ethex
Tags: block, string, upward, velocity
 P: 25 1. The problem statement, all variables and given/known data The force constant of a spring is 600 N/m and the un-stretched length is 0.72m. A 3.2kg block is suspended from the spring. An external force slowly pulls the block down, until the spring has been stretched to a length of 0.86m. The external force is then removed, and the block rises. In this situation, when the spring has the contracted to a length of 0.72m, What is the upward velocity of the block? 2. Relevant equations conservation of energy 3. The attempt at a solution KEinitial + Uinitial = KEfinal + Ufinal 0 + 0.5(600)(0.14)^2 = 0.5 x 3.2 x v^2 + 0 v = 1.92m/s?
 Mentor P: 10,806 Don't forget that gravity is working on the block too!
 P: 25 KEinitial + Uinitial = KEfinal + Ufinal 0 + 0.5(600)(0.14)^2 + (3.2)(9.8)(0.14) = 0.5 x 3.2 x v^2 + 0 Is this right?
Mentor
P: 10,806

## Upward velocity of a block on a string

 Quote by ethex KEinitial + Uinitial = KEfinal + Ufinal 0 + 0.5(600)(0.14)^2 + (3.2)(9.8)(0.14) = 0.5 x 3.2 x v^2 + 0 Is this right?
Better, but should the gravitational PE be negative? (It looks like you're taking the zero reference for it at the unstretched spring level).
 P: 25 Thank you, that is what i am missing out.

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