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Ch 08: Dynamics II: Motion in a Plane
Chapter 8, Problem 8

A satellite orbiting the moon very near the surface has a period of 110 min. What is free-fall acceleration on the surface of the moon? Astronomical data are inside the back cover of the book.

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Identify the given values: The orbital period (T) of the satellite is 110 minutes. Convert this period into seconds for calculations in SI units.
Recall the formula for the orbital period of a satellite: T = 2\pi \sqrt{\frac{r^3}{GM}} where T is the period, r is the radius of the orbit (approximately equal to the radius of the moon for a satellite orbiting very close to the surface), G is the gravitational constant, and M is the mass of the moon.
Rearrange the formula to solve for the gravitational parameter GM: GM = \frac{4\pi^2 r^3}{T^2}.
Substitute the radius of the moon (r) and the period (T) into the equation to find GM. Use the astronomical data provided for the radius of the moon.
Calculate the acceleration due to gravity (g) on the surface of the moon using the formula g = \frac{GM}{r^2}. Substitute the value of GM obtained from the previous step and the radius of the moon to find g.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Orbital Period

The orbital period is the time it takes for an object to complete one full orbit around a celestial body. In this case, the satellite's period of 110 minutes indicates how long it takes to circle the moon. This period is crucial for calculating the gravitational force acting on the satellite, which is directly related to the free-fall acceleration experienced on the moon's surface.
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Gravitational Acceleration

Gravitational acceleration is the acceleration experienced by an object due to the gravitational force exerted by a massive body, such as the moon. On the surface of the moon, this acceleration can be determined using the formula derived from Newton's law of universal gravitation, which relates the mass of the moon and the distance from its center to the surface. It is typically denoted as 'g' and varies depending on the celestial body.
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Newton's Law of Universal Gravitation

Newton's Law of Universal Gravitation states that every point mass attracts every other point mass in the universe with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centers. This law is fundamental for understanding how gravitational forces operate, allowing us to calculate the free-fall acceleration on the moon by relating the satellite's orbital characteristics to the moon's mass and radius.
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