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Homework Statement
This is not an assigned homework problem but could be considered a hw-like problem. I do not have a physics book currently. I looked on Wikipedia, but did not find anything. I posted here in the homework section because I felt the problem may not be general enough for the general physics section.
I'm trying to derive Δmv from a non-constant Force(t) function.
If I have a Force vs. Time graph, the area under the curve is impulse.
I would like to convert [itex]\int^{t_{2}}_{t_{1}}F(t)dt[/itex] into Δmv by u-substitution
Homework Equations
trying to find a u - substitution (or v-substitution) that makes sense.
as in let v = v(t), so dv = v'(t)dt
or let v = t, so dv = t'dt
this is where I'm not making any progress I believe...
The Attempt at a Solution
I = [itex]\int^{t_{2}}_{t_{1}}F(t)dt[/itex] = [itex]\int^{t_{2}}_{t_{1}}m(a(t))dt[/itex] =[itex]\int^{t_{2}}_{t_{1}}m(v'(t))dt[/itex]
Then for substitution, I decided to randomly let v = v(t)
because that's the only way I can get dv = v'(t)dt
so that from here, I can substitute and get:
[itex]m\int^{t_{2}}_{t_{1}}(v'(t))dt[/itex] ==> [itex]m\int^{t_{2}}_{t_{1}}dv[/itex]
But if I change dt to dv, then I have to change [itex]\int^{t_{2}}_{t_{1}}[/itex] to [itex]\int^{v_{2}}_{v_{1}}[/itex] somehow?
The integral [itex]m\int^{v_{2}}_{v_{1}}dv[/itex] seems to equal mv_{2} - mv_{1} = Δmv
However, I don't think I am choosing the right substitution from the start because suppose I have a function:
Force(t) = F(t) = 60t^{2}
[itex]\int^{t_{2}}_{t_{1}}F(t)dt[/itex] = [itex]\int^{4s}_{2s}60t^{2}dt[/itex]
and I want to express the function in terms of velocity, v:
[itex]\int^{v_{2}}_{v_{1}}(?)dv[/itex]
I can't choose v = v(t) because there is no v's in the function to begin with, only t's.
How can I express the Force in terms of time function as simply mv?
P.S.
I already know that [itex]\int F(t)dt[/itex] = [itex]m\int a(t)dt[/itex]
[itex]a\int\frac{dv}{dt}dt[/itex] = [itex]m\int dv[/itex] = Δmv
I am not looking to equate a(t) = dv/dt
I am instead trying to find a substitution such that the limits of the integral reflect velocity values.
So instead of choosing two different times and solving [itex]\int^{t_{2}}_{t_{1}}F(t)dt[/itex]
I guess I'm trying to find be able to choose two different velocities and perhaps solve [itex]m\int^{v_{2}}_{v_{1}}dv[/itex]
I just don't know how to arrive at [itex]m\int^{v_{2}}_{v_{1}}dv[/itex] via the u-substitution method.
P.P.S.
Hope my question makes some sense.
Thank you.
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