Determine the escape velocity from a moon with one-sixth the mass of Earth and a radius one-fourth that of Earth.
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To determine the escape velocity from a moon, we can use the formula for escape velocity:
\[ v_{\text{escape}} = \sqrt{\frac{{2GM}}{{R}}} \]
Where:
- \( v_{\text{escape}} \) is the escape velocity
- \( G \) is the gravitational constant (\( 6.67430 \times 10^{-11} \, \text{m}^3 \, \text{kg}^{-1} \, \text{s}^{-2} \))
- \( M \) is the mass of the moon
- \( R \) is the radius of the moon
We are given that the mass of the moon (\( M \)) is one-sixth the mass of Earth, and the radius of the moon (\( R \)) is one-fourth the radius of Earth. Let's assume the mass of Earth \( M_E = 5.972 \times 10^{24} \, \text{kg} \) and its radius \( R_E = 6.371 \times 10^6 \, \text{m} \).
Therefore, the mass of the moon (\( M_m \)) is \( \frac{1}{6} M_E \) and the radius (\( R_m \)) is \( \frac{1}{4} R_E \).
Substituting these values into the escape velocity formula:
\[ v_{\text{escape}} = \sqrt{\frac{{2G \left(\frac{1}{6} M_E\right)}}{{\left(\frac{1}{4} R_E\right)}}} \]
Simplifying further:
\[ v_{\text{escape}} = \sqrt{\frac{8G M_E}{3 R_E}} \]
Now, we can substitute the known values:
- \( G = 6.67430 \times 10^{-11} \, \text{m}^3 \, \text{kg}^{-1} \, \text{s}^{-2} \)
- \( M_E = 5.972 \times 10^{24} \, \text{kg} \)
- \( R_E = 6.371 \times 10^6 \, \text{m} \)
\[ v_{\text{escape}} = \sqrt{\frac{8 \times 6.67430 \times 10^{-11} \times 5.972 \times 10^{24}}{3 \times 6.371 \times 10^6}} \]
Evaluating this expression gives the escape velocity from the moon.