How can I make this open arc in Sketch?

Question

How can I make like this shape in Sketch3 App?

Answer 1

Let's start from oval with no fill:

Select Edit mode:

Then choose from menu: Layer -> Paths -> Scissors

Hover over left upper part of the oval, it will be dashed:

Left click on it, you will get the following result:

To make the endings rounded select gear icon on border part and select rounded ends:

That's it!

Answer 2

To open up the circle's stroke:

Draw a circle, double-click it, click "Open path" in the sidebar (right below the alignment buttons).

To get the rounded ends:

Click the "Gear" button in the "Borders" section of the sidebar. In the "Ends" button group, choose the rounded one.