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C4 help pleasseeeeeee

Oil is leaking from a storage container onto a flat section of concrete at a rate of
0.48 cm3 s^–1. The leaking oil spreads to form a pool with an increasing circular cross-section. The pool has a constant uniform thickness of 3 mm.
Find the rate at which the radius r of the pool of oil is increasing at the instant when
r = 5 cm. Give your answer, in cm s–1, to 3 significant figures

I don't get why dV/dt is not -0.48cms^-1

Reply 1

Rev16

dV/dt is positive as the question is concerned with the pool of oil, which is getting larger, and not with the container itself (if it was the container then yes, it would be negative). Hope this helps!!!