- #1
roam
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Homework Statement
The following is a solved problem:
http://img600.imageshack.us/img600/6503/questiono.jpg
I can't understand how they worked out these two components.
Homework Equations
[itex]\vec{a}(t) = \frac{dv}{dt}\vec{T} + v \frac{d \vec{T}}{dt}[/itex]
Where
[itex]\vec{T}(t) = \frac{d \vec{r}(t)/dt}{||d \vec{r}(t)/dt||} = \frac{\vec{v}(t)}{v(t)}[/itex]
The Attempt at a Solution
In the equation I posted above, I believe the first term is the tangential component of acceleration and the second one is the normal component. I want first to find the tangential component:
[itex]\vec{v}(t) = d(t^2 \vec{i} + 3t+2 \vec{j})/dt = 2t+3[/itex]
[itex]|| \vec{v}(t) || = \sqrt{4t^2+9}[/itex]
So substituting in
[itex]\frac{dv}{dt}\vec{T} = \frac{d (\vec{r}(t)/dt)}{dt} . \frac{d \vec{r}(t)}{dt}.\frac{1}{||\vec{r}(t)||}[/itex]
[itex]2.(2t+3).\frac{1}{\sqrt{4t^2+9}}[/itex]
[itex]= \frac{4t+6}{\sqrt{4t^2+9}}[/itex]
But this is wrong. The correct answer must be
[itex]\frac{4t}{\sqrt{4t^2+9}}[/itex]
What did I do wrong? How can I get to the correct answer? Any guidance is greatly appreciated.
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