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DV/dS*v = a

by carhah
Tags: acceleration, velocity
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carhah
#1
Jan8-13, 03:45 AM
P: 5
dV/dS*v=a
now at the higest point when we throw a ball.
v=0
which implies a=0

but that is npot true....any expanations?
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tiny-tim
#2
Jan8-13, 03:58 AM
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hi carhah! welcome to pf!
Quote Quote by carhah View Post
v=0
which implies a=0
no, v= 0 does not imply dv/dt = 0

(draw a graph of v against t)
carhah
#3
Jan8-13, 04:04 AM
P: 5
but if we put v=0 in equation-dV/dS*v=a

we get a=0?

i am in doubt...

carhah
#4
Jan8-13, 04:06 AM
P: 5
DV/dS*v = a

Quote Quote by tiny-tim View Post
hi carhah! welcome to pf!


no, v= 0 does not imply dv/dt = 0

(draw a graph of v against t)

but if we put v=0 in equation-dV/dS*v=a
tiny-tim
#5
Jan8-13, 04:26 AM
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hi carhah!

(you don't need to send a pm everyone gets automatic email notification of any new post in any thread they've posted in )
Quote Quote by carhah View Post
but if we put v=0 in equation-dV/dS*v=a
but dv/ds = ∞ (draw the graph of v against s)

eg, if a is constant, and if so = vo = 0, then s = 1/2 at2 and v = at,

so v = √(2as), so dv/ds|t=0 = √(a/so)= √(a/0) = ∞
carhah
#6
Jan8-13, 04:35 AM
P: 5
Quote Quote by tiny-tim View Post
hi carhah!

(you don't need to send a pm everyone gets automatic email notification of any new post in any thread they've posted in )


but dv/ds = ∞ (draw the graph of v against s)

eg, if a is constant, and if so = vo = 0, then s = 1/2 at2 and v = at,

so v = √(2as), so dv/ds|t=0 = √(a/so)= √(a/0) = ∞



thanks tim :D
BUT DOES that mean that we cannot apply that formula a=dv/ds*v in case of constant acceleration. :)
tiny-tim
#7
Jan8-13, 04:42 AM
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Quote Quote by carhah View Post
thanks tim :D
BUT DOES that mean that we cannot apply that formula a=dv/ds*v in case of constant acceleration. :)
no, you can always apply that formula
but if it says a = ∞*0, that doesn't help very much!
carhah
#8
Jan8-13, 05:02 AM
P: 5
can u draw graph of dv/ds ? and prove it is infinity?
tiny-tim
#9
Jan8-13, 05:26 AM
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Quote Quote by carhah View Post
can u draw graph of dv/ds ?
you can draw a graph of v against s (as i've already asked you to)
where it's vertical, dv/ds = ∞


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