A electric model train travels at 0.339 m/s around a circular track of radius 1.75 m. How many revolutions does it perform per second, i.e, what is the motion's frequency?
Cheap way to get to the answer if you understand what the problem asks for you is to look at what you have in units and see what units you need the answer to be at the end. In this case you know the speed, and you can find the circumference (i.e the distance it has to travel). And you know it's asking for a frequency which should be in Hertz or 1/s.
In this case you find the circumference using L=2*pi*R (radius) and then divide the speed (m/s) by the distance (m) and you should get a frequency (1/s). I hope this clears up a bit.