What is the perimeter of a semicircle with radius 8cm?

A semicircle is half a circle. So the perimeter of a semicircle is half the circumference of the whole circle plus the diameter, which is twice the radius:

perimeter = 1/2 x 2{pi}r + 2r

perimeter ~= 3.14x8 + 2x8 ~= 41.13cm