I am working on the following physics problem and I want to enter a quantity for plane angle that I will convert to radians and degrees for comparison:
25*(II) A car at the Indianapolis 500 accelerates uniformly from the pit area, going from rest to 270 km/h in a semicircular arc with a radius of 220 m. Determine the tangential and radial acceleration of the car when it is halfway through the arc, assuming constant tangential acceleration. If the curve were flat, what coefficient of static friction would be necessary between the tires and the road to provide this acceleration with no slipping or skidding?
I tried

UnitConvert[
 Quantity[1, "Revolutions"], {"Radians", "Milliradians", "Degrees"}]

but Mathematica returned

{$Failed, $Failed, $Failed}

I realize the issue is that the dimensions are different.

AssociationMap[UnitDimensions][{Quantity[1, "Revolutions"], 
  Quantity[1, "Radians"], Quantity[1, "Milliradians"], 
  Quantity[1, "AngularDegrees"]}]

I think there is an angle unit to enter as fractions of a circle. For example, I tried revolutions when I found the unit to convert from at https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9#ANGLE. I also thought maybe the name of the quantity was cycle, but that doesn't work either. I also tried circle and that didn't work. If there was a way to list all the quantities supported by Quantity like how FormulaData[] lists all the formulas, I could use the operator form

Select[CompatibleUnitQ[#, "AngularDegrees"] &]

to find all the unit compatible with radians. Is there a way to list all the quantities supported by Quantity.

I entered convert convert 5 mrad to revolutions into Wolfram Alpha and it returned computable data with Quantity and "Revolutions". I found a way to compute the semicircle with Region:

Region[Circle[{0, 0}, 220, {0 Degree, 180 Degree}]]

This draws half of the semicircle:

Region[Circle[{0, 0}, 220, {90 Degree, 180 Degree}]]

The arc length of the semicircle:

In[267]:= FullSimplify[
 RegionMeasure[
  Region[Circle[{0, 0}, Quantity[220, "Meters"], {0 Degree, 180 Degree}]]]]

Out[267]= Quantity[220 \[Pi], "Meters"]

The arc length of half of the semicircle:

In[268]:= FullSimplify[
 RegionMeasure[
  Region[Circle[{0, 0}, Quantity[220, "Meters"], {90 Degree, 180 Degree}]]]]

Out[268]= Quantity[110 \[Pi], "Meters"]