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Socrates
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Homework Statement
A dustpan slides down a plane inclined at angle θ. Dust is uniformly dis- tributed on the plane, and the dustpan collects the dust in its path. After a long time, what is the acceleration of the dustpan? Assume there is no friction between the dustpan and plane.
p=linear mass density of dust
x is chosen as distance along the plane
Homework Equations
d(mv)/dt=mgsin(θ) (net force parallel to the plane)
m(x)=px
The Attempt at a Solution
My solution:
d(mv)/dt=mdv/dt+vdm/dt=mgsin(θ)
dm/dt=pdx/dt=pv
dv/dt=x''
direct substitution:
px*x''+p(x')^2=pxgsin(θ)
xx''+(x')^2-xgsin(θ)=0
Dimensional analysis: x(g, t, θ) must be of the form:
x=Agt^2
x'=2Agt
x''=2Ag
Substitute into DiffEq:
2A^2g^2t^2+4A^2g^2t^2-Ag^2t^2sin(θ)=0
cancel g^2t^2
6A^2-Asin(θ)=0
A=sin(θ)/6
x''=gsin(θ)/3My question is, is this reasoning correct?
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