The arc length is the measure of the distance along the curved line making up the arc. It is longer than the straight line distance between its endpoints. To calculate this we simply multiply the angle to the circumference of the circle. It is expressed as:
Arc length = 2πr(angle / 360)
Arc length = 2πr(50 / 360)
Arc length = 5πr / 18
Just multiply the radius then you're good. Hope this helps. Have a nice day.