Help, Dynamics, Rectilinear knematics

vcantu04

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Mar 23, 2005
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problem is A train traveling a straight track at 2m/s, begins too accelerate a=(60v^-4)m/s^2, where v is in m/s. Determine its velocity and position 3s after the acceleration.

This is what I have.

a=dv/dt, int(dv/a)=int(dt)
integral from 2(m/s) to v of (dv/60v^-4) = integral of tdt from 0 to t.
then t=60[(v^5)/5] evaluated from 2 to v.
finally t = 12(v^5 - 32).
Solving for v, v=(t/12 +32)^(1/5) and substituting for t=3, v=2.003 m/s. (I am not sure about the V @ 3s, value seems to small).

To obtain the positions @ 3s:
v=ds/dt intds=intvdt
int from 0 to s of ds = int from 0 to t of (32+t/12)^(1/5)dt
s=[5/(1/12)]{32+t/12}^1/5 evaluated from 0 to t and @ t=3,
s=0.186

I think the values are too small so I wil appreciate if somebody can check the solutions.

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Before going thru your math, s after 3 seconds must be greater than v<sub>0</sub>t = 2m/s*3s = 6m so you know you went astray.
I get
Int(dv/a) =
int(dv/(60v^(-4))) = (1/60)int(v^(4)dt)
A minor slip.
Is that enough?
 
Thanks Gene you are really helpful. @ 3 s for v I got 3.92m/s and s=10.15m.
 
Looks good to me though s may be a smidgen high. Don't round v till you have s. And v when rounded is 3.93
All in all, Nice Job.
-------------------
Gene
 
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