circle solid

Question

The base of a solid is the circle x2 + y2 = 9. Cross sections of the solid perpendicular to the x-axis are semi-circles. What is the volume, in cubic units, of the solid? (2 points)

9x/4

18π

9π

72π

Answer 1

It's impossible to draw here but it's just saying is a hemisphere (half of a sphere) with radius of 3 (Since the standard equation of a circle is x² + y² = r², you can say that r² = 9 hence r = 3).

 

The volume of sphere is V = (4/3)*Π*r³ so the volume of a hemisphere is V = (2/3)*Π*r³

 

V = (2/3)*Π*(3)³ = 18Π c.u.