Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta
    • Thread Starter
    Offline

    1
    ReputationRep:
    Hey, can you check my working for this question please. :

    "The volume of a sphere is increasing at a rate of 75cm^3/s. Find the rate at which the radius is increasing at the instant when the radius of the sphere is 15cm."

    My working :

    dv/dt = 75

    v = 4/3*pi*r^3

    dv/dr = 4*pi*r^2

    dr/dt = dr/dv * dv/dt

    Therefore dr/dt = 75/(4*pi*r^2)

    When r = 15

    dr/dt = 0.0265

    Is this right? any comments will be appreciated. Thanks.
    Offline

    2
    ReputationRep:
    looks right to me (but i've not checked things like your muliplication)

    good luck tomorrow!

    lou xxx
 
 
 
Poll
Do you agree with the proposed ban on plastic straws and cotton buds?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.