# Homework Help: Calc AB Related Rates Problem

1. Feb 7, 2012

### pry_or

1. The problem statement, all variables and given/known data

A container of constant volume contains a quantity of gas under pressure. At t=0, the pressure is 4 psi and the temperature is 15°C per minute. What is the rate of change of the pressure inside the container at time t=0?

2. Relevant equations

$\frac{P}{T}$ = constant

3. The attempt at a solution

Taking the derivative of both sides and then simplifying, I ended up with:

T$\frac{dP}{dT}$ - P$\frac{dT}{dT}$ = 0

So solving for dP/dt:

$\frac{dP}{dt}$ = $\frac{P}{T}$$\frac{dT}{dt}$

This is where I get stuck. I know P = 4 psi and dT/dt = 15°C per minute, but I can't figure out how to determine T. Without knowing the actual value of the constant in the original formula, I don't see how it is possible. The wording of the temperature value in the problem sounds odd to me. The only thing I can think of is that the temperature should be assumed to be 0°C at t=0 and so dP/dt does not exist. Is this it, or am I missing some way to find T?

2. Feb 7, 2012

### Staff: Mentor

15°C per minute is not a temperature. It's the time rate of change of temperature. What is the exact wording of this problem?

3. Feb 7, 2012

### pry_or

That is the exact wording of the problem. That's why I said the wording was odd.

4. Feb 7, 2012

### Staff: Mentor

Whoever wrote the problem made a mistake. I would get some clarification from the instructor as to what the real problem is.

5. Feb 7, 2012

### pry_or

That's what I expected, thank you!

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook