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# A2 maths core 3. HELPPP!! watch

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1. i am struggling with differentiation: rate of change.

a funnel has a circular top of diameter 20cm and a height of 30cm. when the depth of liquid in funnel is 15cm, the liquid is dripping from the funnel at a rate of 0.2cm^3s^-1. at what rate is the depth of the liquid in the funnel decreasing at this instant?
2. (Original post by alosky)
i am struggling with differentiation: rate of change.

a funnel has a circular top of diameter 20cm and a height of 30cm. when the depth of liquid in funnel is 15cm, the liquid is dripping from the funnel at a rate of 0.2cm^3s^-1. at what rate is the depth of the liquid in the funnel decreasing at this instant?
Funnel = cone = right cone = similar triangles
you have dv/dt
you want dh/dt
can you make a chain? do you know/need the equation of a right cone?/can you use similar triangles to express h in terms of r (height and radius)?

Chuck something together using similar triangles and see what happens.

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Updated: October 1, 2011
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