Turn on thread page Beta
    • Thread Starter

    I'm not sure if what I've done so far is correct but I can't figure what to do next.

    Each edge of a contracting cube is decreasing at a rate of 0.06cms^-1.
    Find rate of decrease of the volume.

    Here's what Ive done:
    dv/dt = dx/dt x dv/dx

    v = x^3
    dv/dx = 3x^2
    Sub in

    dv/dt = 0.06 x 3x^2
    dv/dt = 0.18x^2

    Here is where I get stuck, I tried to find value for x but am not getting correct answer.
    Thanks for any help.

    You said both v and x are functions of time to you'd want v on the RHS of your last equation. I haven't done this in a long time, but i presume you have \dfrac{dv}{dt}=f(v(t)) where f(v(t))=\sqrt[3]{v} and solve as usual. substitute x back in afterwards because you know the relationship
    • Thread Starter

    Ok, thanks for your help.
Submit reply
Turn on thread page Beta
Updated: February 11, 2010
The home of Results and Clearing


people online now


students helped last year

University open days

  1. Sheffield Hallam University
    City Campus Undergraduate
    Tue, 21 Aug '18
  2. Bournemouth University
    Clearing Open Day Undergraduate
    Wed, 22 Aug '18
  3. University of Buckingham
    Postgraduate Open Evening Postgraduate
    Thu, 23 Aug '18
A-level students - how do you feel about your results?
Useful resources

Make your revision easier


Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here


How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

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