Earth Moon Ratios
1. Problem 22 states:
Given the Earth's mean radius $r_\text{Earth} = 6.37 \times 10^{6} \ m$ and Moon's mean radius $r_\text{Moon} = 1.74 \times 10^{8} \ cm$, calculate:
(a) The ratio of Earth's surface area to Moon's surface area.
(b) The ratio of Earth's volume to Moon's volume.
Note: Convert Moon's radius to meters because SI units must be consistent.
2. Convert Moon's radius from cm to m:
$$r_\text{Moon} = 1.74 \times 10^{8} \ {cm} \times \left( \frac{1 \ m}{100 \ cm} \right) = 1.74 \times 10^{6} \ m$$
3. Recall surface area formula for a sphere:
$$S = 4 \pi r^{2}$$
Calculate the surface areas:
$$S_\text{Earth} = 4 \pi (6.37 \times 10^{6})^{2}$$
$$S_\text{Moon} = 4 \pi (1.74 \times 10^{6})^{2}$$
Find the ratio:
$$\frac{S_\text{Earth}}{S_\text{Moon}} = \frac{4 \pi (6.37 \times 10^{6})^{2}}{4 \pi (1.74 \times 10^{6})^{2}} = \left( \frac{6.37 \times 10^{6}}{1.74 \times 10^{6}} \right)^{2} = \left( \frac{6.37}{1.74} \right)^{2}$$
Calculate numeric value:
$$\frac{6.37}{1.74} \approx 3.66$$
So,
$$\frac{S_\text{Earth}}{S_\text{Moon}} = 3.66^{2} = 13.4$$
4. Recall volume formula for a sphere:
$$V = \frac{4}{3} \pi r^{3}$$
Calculate volumes:
$$V_\text{Earth} = \frac{4}{3} \pi (6.37 \times 10^{6})^{3}$$
$$V_\text{Moon} = \frac{4}{3} \pi (1.74 \times 10^{6})^{3}$$
Find the ratio:
$$\frac{V_\text{Earth}}{V_\text{Moon}} = \frac{(6.37 \times 10^{6})^{3}}{(1.74 \times 10^{6})^{3}} = \left( \frac{6.37}{1.74} \right)^{3} = 3.66^{3}$$
Calculate numeric value:
$$3.66^{3} = 49.0$$
5. Final answers:
(a) Ratio of surface areas = $13.4$
(b) Ratio of volumes = $49.0$
These ratios show Earth has about 13.4 times the surface area and 49 times the volume of the Moon.