What is the tangential acceleration of a toy car at a specific point in a loop?

[heartyface]

Homework Statement

Perhaps I am confused by the concept.
A toy car starts from rest at a height 4R above the ground and continue to a loop of radius R (frictionless). At a point C (height R from the ground) inside the loop, what is the tangential acceleration of the toy car?

Homework Equations

I don't think a=alpha*r is quite relevant to this...or a=dv/dt...

The Attempt at a Solution

not quite yet. perhaps the gravity is the only thing?

Please, explain me of the concept of 'tangential acceleration' and its components.

 

[haruspex]

Tangential acceleration is simply the component of linear acceleration that's in the tangential direction. You are right that this is not the same as angular acceleration * radius, r\dot{ω}. There is also the Coriolis term 2\dot{r}ω.
It's not quite clear from the question (the position of the loop in relation to the ground is not given): is point C where the loop is vertical?

 

[tiny-tim]

(this is the same as https://www.physicsforums.com/showthread.php?t=661829)