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- #1

#### karush

##### Well-known member

- Jan 31, 2012

- 2,820

on b) I think this is the point they wanted us to get

hope answers are correct its an even problem # so no ans in bk.

- Thread starter karush
- Start date

- Thread starter
- #1

- Jan 31, 2012

- 2,820

on b) I think this is the point they wanted us to get

hope answers are correct its an even problem # so no ans in bk.

- Admin
- #2

Your results for part a) are correct.

In your working, where you evaluate \(\displaystyle \frac{dV}{dt}\) for the given values of $r$, you should have replaced \(\displaystyle \frac{dr}{dt}\) with \(\displaystyle 3\,\frac{\text{in}}{\text{min}}\) instead of \(\displaystyle 3\text{ in}\). Also, I think what they are looking for in part b) is that \(\displaystyle \frac{dV}{dt}\) is proportional to the square of $r$. Thus it changes quadratically, not exponentially.