Register to reply

Upward velocity of a block on a string

by ethex
Tags: block, string, upward, velocity
Share this thread:
ethex
#1
Sep29-11, 09:54 AM
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?
Phys.Org News Partner Science news on Phys.org
Scientists develop 'electronic nose' for rapid detection of C. diff infection
Why plants in the office make us more productive
Tesla Motors dealing as states play factory poker
gneill
#2
Sep29-11, 11:02 AM
Mentor
P: 11,689
Don't forget that gravity is working on the block too!
ethex
#3
Sep29-11, 11:20 AM
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?

gneill
#4
Sep29-11, 11:31 AM
Mentor
P: 11,689
Upward velocity of a block on a string

Quote Quote by ethex View Post
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).
ethex
#5
Sep29-11, 11:43 AM
P: 25
Thank you, that is what i am missing out.


Register to reply

Related Discussions
Object thrown upward with known initial and final velocity Introductory Physics Homework 6
Block suspended on a string Introductory Physics Homework 17
Minimum string tension needed to move the block Introductory Physics Homework 20
Maximum Upward Acceleration of a String Introductory Physics Homework 2
Given height, and velocity thrown upward, find air-time Introductory Physics Homework 8