PLease help for differential equation

AI Thread Summary
The differential equation \(\frac{dy}{dt} = \frac{1}{(y+2)^{2}}\) with initial condition \(y(0) = 1\) leads to the solution \(y(t) = \sqrt[3]{3t-27} - 2\). The domain of this solution is restricted to \(t \geq 0\) due to the initial condition, despite the cube root function having a domain of all real numbers. As \(t\) approaches infinity, the solution approaches a limit of 2. The solution cannot be extended to negative \(t\) values because it would result in undefined values under the cube root. Thus, the solution is valid only for non-negative \(t\).
stunner5000pt
Messages
1,443
Reaction score
4
\frac{dy}{dt} = \frac{1}{(y+2)^{2}} and y(0) =1

th solution i got is y(t) = \sqrt[3]{3t-27} - 2

the question asks find the domain of the definition of the solution

Describe hwat happens when the solution as it reaches it'slimits of its domain. Why can't it be extended for more time?

Looking at he function aid ti s CUBE ROOT shouldn't the domain be ALL REAL number?? So the limits are positive and negative infinity? So then the limits are positive and negative infinity respeectively??

Input would be greatly valued! Thank you!@
 
Last edited:
Physics news on Phys.org
If you've typed your DE correctly then I think you have the wrong sign on the constant 27. Other than that, the derivative is undefined when y = -2 which occurs at t = -9 and makes it impossible to extend your soluion to t <= 9.
 


The solution you have obtained for the given differential equation is correct. However, the domain of the solution is not all real numbers. In order to find the domain, we need to consider the restrictions on the variable t and the initial condition given.

In this case, the variable t must be greater than or equal to 0 since the initial condition is given at t=0. This means that the solution is only defined for t values greater than or equal to 0. As t approaches infinity, the solution will approach a limit of 2. This is because as t becomes larger, the cube root term in the solution will dominate and the solution will approach 2. This is also evident from the given initial condition, y(0)=1, which is less than 2.

The reason why the solution cannot be extended for more time is because it is only defined for t values greater than or equal to 0. If we try to plug in a negative t value, we will get a negative number under the cube root, which is not defined in the real numbers. This is why the domain of the solution is limited to t greater than or equal to 0.

It is important to note that the cube root function has a domain of all real numbers, but in this case, the variable t is restricted to non-negative values due to the given initial condition. Therefore, the solution is only valid for t values in the non-negative domain.

I hope this clarifies any confusion. Keep up the good work in solving differential equations!
 
TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
Thread 'Variable mass system : water sprayed into a moving container'
Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
Back
Top