Mensuration Questions

Multiple choice
  1.  $6\displaystyle cm^{2}$
  2. $5.16\displaystyle cm^{2}$
  3. $5.9973\displaystyle cm^{2}$
  4. $5.71\displaystyle cm^{2}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The 3 cm, 4 cm, 5 cm triangle is right-angled, so its area is (3 x 4)/2 = 6 cm^2. Each hole has radius 0.3 cm, and the total area removed is 3 x pi x 0.3^2, approximately 0.848 cm^2. The remaining area is approximately 6 - 0.848 = 5.16 cm^2.

Multiple choice
  1. $\displaystyle \dfrac 4 {\pi} $
  2. $\displaystyle \dfrac  {\pi} 4 $
  3. $\displaystyle \pi $
  4. $\displaystyle {\pi}^{2} $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A sheet of area 2 rolled into a cylinder implies the lateral surface area is 2 = 2*pi*r*h. Volume = pi*r^2*h = 4/pi. From the first, h = 1/(pi*r). Substituting into volume: pi*r^2*(1/(pi*r)) = r = 4/pi.

Multiple choice
  1. $5.66a^3$
  2. $1.33a^3$
  3. $2.66a^3$
  4. $7.40a^3$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In hcp/ccp, the packing efficiency is 74%. The volume of the unit cell is V_cell. The number of spheres per unit cell is 4. Volume of 4 spheres = 4 * (4/3) * pi * a^3 = 16/3 * pi * a^3. V_cell = (16/3 * pi * a^3) / 0.74 = 22.67 * a^3. The question asks for volume per sphere = V_cell / 4 = 5.66 * a^3.