- #1
Sneakatone
- 318
- 0
Homework Statement
A 4-pound weight stretches a spring 2 feet. The weight is released from rest 15 inches above the equilibrium position, and the resulting motion takes place in a medium offering a damping force numerically equal to 7/8 times the instantaneous velocity. Use the Laplace transform to find the equation of motion x(t). (Use g = 32 ft/s2 for the acceleration due to gravity.)
Homework Equations
my''+(beta)y'+ky=0
m=4/32=1/8
beta=7/8
k=4/2=2
The Attempt at a Solution
1/8y''+7/8y'+2y=0, y(0)=-18, y'(0)=0
I know the answer which is:
-1/10e^(-7t/2)[7√(15)sin(√(15)t/2)+15cos(√(15)t/2)]
https://www.webassign.net/latexImages/5/f/f1c0fb013b3d1d7c4fddd1209a1d60.gif
but my awnser came out to be:
http://www4c.wolframalpha.com/Calculate/MSP/MSP104701e9a70abfi51f43a000045edi0bi5e950fi2?MSPStoreType=image/gif&s=14&w=373.&h=45 .
which makes me fell like my y'(0) is incorrect. I would think that y'(0) would be a valid initial condition but the problem seem to not state anymore about velocity.
Last edited by a moderator: