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Ch. 08 - Conservation of Energy
Giancoli Douglas - Physics for Scientists and Engineers 5th edition
Giancoli Douglas5th editionPhysics for Scientists and EngineersISBN: 9780137488179Not the one you use?Change textbook
Chapter 8, Problem 44a

Determine the escape velocity from the Sun for an object at the Sun’s surface ( r = 7.0 x 10⁵ km , M = 2.0 x 10³⁰ kg).

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Step 1: Recall the formula for escape velocity, which is derived from the conservation of energy. The escape velocity \( v_e \) is given by \( v_e = \sqrt{\frac{2GM}{r}} \), where \( G \) is the gravitational constant \( 6.674 \times 10^{-11} \ \text{m}^3 \text{kg}^{-1} \text{s}^{-2} \), \( M \) is the mass of the Sun, and \( r \) is the distance from the center of the Sun to the object.
Step 2: Convert the given radius \( r \) from kilometers to meters. Since \( 1 \ \text{km} = 1000 \ \text{m} \), multiply \( r = 7.0 \times 10^5 \ \text{km} \) by \( 1000 \) to get \( r = 7.0 \times 10^8 \ \text{m} \).
Step 3: Substitute the given values into the escape velocity formula. Use \( G = 6.674 \times 10^{-11} \ \text{m}^3 \text{kg}^{-1} \text{s}^{-2} \), \( M = 2.0 \times 10^{30} \ \text{kg} \), and \( r = 7.0 \times 10^8 \ \text{m} \). The formula becomes \( v_e = \sqrt{\frac{2 \cdot (6.674 \times 10^{-11}) \cdot (2.0 \times 10^{30})}{7.0 \times 10^8}} \).
Step 4: Simplify the numerator \( 2 \cdot G \cdot M \) and the denominator \( r \) separately. Then divide the numerator by the denominator to find the value inside the square root.
Step 5: Take the square root of the result from Step 4 to find the escape velocity \( v_e \). Ensure the units are consistent throughout the calculation, and the final velocity will be in meters per second (m/s).

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Key Concepts

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

Escape Velocity

Escape velocity is the minimum speed an object must reach to break free from the gravitational pull of a celestial body without any additional propulsion. It is derived from the balance between kinetic energy and gravitational potential energy, and is given by the formula v = √(2GM/r), where G is the gravitational constant, M is the mass of the body, and r is the radius from the center of the mass.
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Gravitational Constant (G)

The gravitational constant, denoted as G, is a fundamental physical constant that quantifies the strength of gravitational attraction between two masses. Its value is approximately 6.674 × 10⁻¹¹ N(m/kg)². This constant is crucial in calculations involving gravitational forces and escape velocity, as it directly influences the gravitational potential energy of an object near a massive body.
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Mass and Radius of the Sun

The mass and radius of the Sun are essential parameters in calculating escape velocity. The Sun's mass (approximately 2.0 x 10³⁰ kg) determines the strength of its gravitational field, while its radius (about 7.0 x 10⁵ km) defines the distance from its center at which the escape velocity is being calculated. These values are critical for applying the escape velocity formula accurately.
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