Any system can be modeled using first order differential equation?

Most systems can be modeled using first order system just like a temperature control system of an incubator.

Question 1: How can we know that a certain system can be modeled using first order differential equation?

a1dydt+a0y=F(t)a_1\frac{dy}{dt} + a_0y = F(t)\tag{1}

A first order differential equation in Equation (1) may be written as:

τdydt+y=kF(t)\tau\frac{dy}{dt}+y = kF(t)\tag{2}

Question 2: If a step input

F(t)={0,if t < 0A,if t > 0F(t) =
\begin{cases}
0, & \text{if $t$ < 0} \\ A, & \text{if $t$ > 0}
\end{cases}\tag{3}

of the system has an output response of a

y(t)=kA(1âˆ′eâˆ′tد„)y(t) = kA( 1âˆ’ e^\frac{âˆ’t}{د„}) \tag{4}

then the system can be modeled as first differential equation where

ymax=kAy_{max} = kA\tag{5}

Is this correct?

Given a step input and the graph of the step response of the system. Am i correct if I say that if the output of the system behaves similar to equation (4), then I can model the system using first differential equation?

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