# 12.2.2 Solid Geometry (II), PT3 Focus Practice

                         
12.2.2 Solid Geometry (II), PT3 Focus Practice
 
  Question 5:
  Sphere below has a surface area of 221.76 cm2.
 
 
 Calculate its radius.
                          $\left(\pi =\frac{22}{7}\right)$                        
 
  Solution:
  Surface area of sphere = 4πr2
                          $\begin{array}{l}4\pi {r}^{2}=221.76\\ 4×\frac{22}{7}×{r}^{2}=221.76\\ {r}^{2}=\frac{221.76×7}{4×22}\\ {r}^{2}=17.64\\ r=\sqrt{17.64}\\ r=4.2\text{cm}\end{array}$                      
 
 
 
                         
Question 6:
  Diagram below shows a right pyramid with a square base.
 
 Given the height of the pyramid is 4 cm.
  Calculate the total surface area, in cm2, of the right pyramid.
 
  Solution:
 h2 = 32 + 42
  = 9 + 16
  = 25
  h = √25   = 5 cm2
 
  Total surface area of the right pyramid
  = Base area + 4 (Area of triangle)
  = (6 × 6) + 4 × 4 (½ × 6 × 5)
  = 36 + 60
  = 96 cm2
 
 
 
         
Question 7:
 
Diagram below shows a prism.
 
 Draw to full scale, the net of the prism on the grid in the answer space. The grid has equal squares with sides of 1 unit.
 
 Solution: