- #1
Sheen91
- 27
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Homework Statement
[PLAIN]http://img231.imageshack.us/img231/636/question2m.jpg [Broken]
Homework Equations
v = [tex]\dot{r}[/tex] [tex]\hat{r}[/tex] + r[tex]\dot{\vartheta}[/tex] [tex]\hat{\vartheta}[/tex]
The Attempt at a Solution
[tex]\dot{r}[/tex] = ?
\vartheta = 80°
v = 55mm/s
So I guess I just use the formula above.
v = [tex]\dot{r}[/tex] [tex]\hat{r}[/tex] + r[tex]\dot{\vartheta}[/tex] [tex]\hat{\vartheta}[/tex]
55² = [tex]\dot{r}[/tex]² + rΘ'
And so you try and solve for [tex]\dot{r}[/tex]
r'² = 55² - (r*Θ')²
r' = sqrt(55² - (r*Θ')²)
And then I get stuck. I am either missing something. Or not doing something right. I guess this isn't really r theta, it is more a conversion from r theta to x-y.
Not 100% sure how to do that though.
Cheers
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