ATAR Notes: Forum

VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Specialist Mathematics => Topic started by: tcg93 on October 20, 2010, 09:32:57 pm

Title: Related Rates/Tank problem
Post by: tcg93 on October 20, 2010, 09:32:57 pm

Why is the answer C?

Title: Re: Related Rates/Tank problem
Post by: Stormer on October 20, 2010, 09:45:42 pm

dv/dt=2-kRootH
V=nr^2h

nr^2=2
V=2h

dv/dh = 2
dh/dv=1/2

dh/dt = dv/dt x dh/dv

=1/2 x 2-kRootH

Title: Re: Related Rates/Tank problem
Post by: tcg93 on October 20, 2010, 10:46:17 pm

Quote from: Stormer on October 20, 2010, 09:45:42 pm

dv/dt=2-kRootH
V=nr^2h

nr^2=2
V=2h

dv/dh = 2
dh/dv=1/2

dh/dt = dv/dt x dh/dv

=1/2 x 2-kRootH

Why is dv/dt=2-kRootH ??

Isn't it only fresh water being poured in so you're meant to exclude that?

Title: Re: Related Rates/Tank problem
Post by: mark_alec on October 20, 2010, 11:21:51 pm

Quote from: tcg93 on October 20, 2010, 10:46:17 pm

Isn't it only fresh water being poured in so you're meant to exclude that?

The salt is irrelevant for this question, as they just want to know the change in height with respect to time.

If they asked you to model the mass of salt as a function of time, it would be different.

Title: Re: Related Rates/Tank problem
Post by: Martoman on October 20, 2010, 11:29:23 pm

yeah exactly my thoughts. Its a trick.