A Thin Wire Is Bent into the Shape of a Semicircle

Multiple Choice

A thin wire is bent into the shape of a semicircle $x ^ { 2 } + y ^ { 2 } = 4 , x > 0$ . If the linear density is 4 , find the exact mass of the wire.
Select the correct answer.

A) $3 \pi$
B) $8 \pi$
C) $8 \pi ^ { 2 }$
D) $18 \pi$
E) $2 \pi$