First Order Transients, RC circcuit response DC voltage

[Verris]

So this is an example given to me in one of the guides. I am somewhat confused as to why R and R1 are considered parallel when the switch is closed at t=0.
I thought that the two resistors cannot be parallel since there is a voltage source between them.
One hypothesis I had was to treat it like a thevenin circuit and short circuit VS, but I'm not sure if that's a correct assumption.
Would really appreciate some insight as to why they are considered parallel, thank you.

 

[gneill]

Hi Verris,

Welcome to Physics Forums.

In future please be sure to use the provided formatting template when posting homework help requests in the homework forums. This is explained in the forum guidelines which you were invited to read when you joined.

I thought that the two resistors cannot be parallel since there is a voltage source between them.
One hypothesis I had was to treat it like a thevenin circuit and short circuit VS, but I'm not sure if that's a correct assumption.

Your Thevenin idea has merit. In this situation you need to find the time constant for the RC network, and to do that you will want to know what equivalent resistance the capacitor "sees". So treat the capacitor as the load of the network and find the Thevenin equivalent that drives it.