Maximum charge differential equation

[greg997]

Hi, I am having a small problem with this equation

Charge Q=t^3+5t^2+10t+130

What is the maxiumum charge?
If I differentiate with repect to time, at t=6, for example then I have value of current flowing at that time.
What is the maximum charge then? I don't understand the question. Do I need to differentaite it again? Thanks

 

[grzz]

At maximum Q, dQ/dt = 0.

But, so long as there is no mistake in the equation given, there is no value of t for which dQ/dt = 0.

 

[greg997]

The equation has some value changed by me, but if dQ/dt=0 then the current is 0. Is that right?. About the equation, if I differentiate Q, then I can have two roots t. If I substitute them in the Q equation I have two real, different values. Is that right? Do I choose the higher value obtained?

 

[HallsofIvy]

A quadratic equation can have 2, 1, or no real roots. Read what grzz said again. Are there limits on the values of t?

 

[greg997]

No, there are no limits.I know that quadratic equation can have 2,1, or no ral roots. But in this case it has two different real ones.

 

[NascentOxygen]

Charge Q=t^3+5t^2+10t+130

What is the maxiumum charge?

Each term on the right hand side increases with time, and these are all summed. So Q continuously increases with time. It will reach a maximum only at the end of time.

I don't understand the question.

I think it's worth taking another look at the question. Something might be amiss.

 

[SammyS]

Hi, I am having a small problem with this equation

Charge Q=t^3+5t^2+10t+130

What is the maximum charge?
If I differentiate with respect to time, at t=6, for example then I have value of current flowing at that time.
What is the maximum charge then? I don't understand the question. Do I need to differentiate it again? Thanks

It asks for maximum charge, so just differentiate once. Yes, it so happens that when dQ/dt = 0 , in addition to having maximum (or minimum) charge, the current is also zero, because current = dQ/dt .