If the radius of a planet is \(\alpha\) times the radius of the earth and its mass \(\beta\) times that of the earth, find the ratio of the acceleration of the force of gravity and the first and second cosmic velocities to the corresponding quantities for the earth.

Short Answer

Expert verified
Answer: The ratios are as follows: Gravitational acceleration ratio: \(\frac{β}{α^2}\) First cosmic velocity ratio: \(\sqrt{\frac{β}{α}}\) Second cosmic velocity ratio: \(\sqrt{\frac{β}{α}}\)

Step by step solution

01

Find the acceleration due to gravity on the planet

To find the gravitational acceleration on the planet, we will use the formula: \(g = \frac{GM}{R^2}\) where G is the gravitational constant, M is the mass of the planet, and R is its radius. Since the mass of the planet is β times the Earth's mass (Me) and its radius is α times the Earth's radius (Re), we have: \(g_p = \frac{G\cdot(βM_e)}{(αR_e)^2}\)
02

Calculate the first cosmic velocity for the planet

The first cosmic velocity (orbital velocity) for the planet can be found using the following formula: \(v_{1_p} = \sqrt{\frac{GM}{R}}\) Substituting the values for the planet's mass and radius, we get: \(v_{1_p} = \sqrt{\frac{G\cdot(βM_e)}{αR_e}}\)
03

Calculate the second cosmic velocity for the planet

The second cosmic velocity (escape velocity) for the planet is given by the formula: \(v_{2_p} = \sqrt{\frac{2GM}{R}}\) Substituting the values for the planet's mass and radius, we get: \(v_{2_p} = \sqrt{\frac{2G\cdot(βM_e)}{αR_e}}\)
04

Find the ratios of gravitational acceleration and cosmic velocities for the planet and Earth

Now, we need to find the ratio of the gravitational acceleration, first cosmic velocity, and second cosmic velocity for the planet to the corresponding quantities for Earth. The gravitational acceleration on Earth is: \(g_e = \frac{GM_e}{R_e^2}\) Thus, the ratio of gravitational acceleration for the planet and Earth is: \(\frac{g_p}{g_e} = \frac{\frac{G\cdot(βM_e)}{(αR_e)^2}}{\frac{GM_e}{R_e^2}} = \frac{βM_e}{α^2R_e^2}\cdot\frac{R_e^2}{M_e} = \frac{β}{α^2}\) The first cosmic velocity on Earth is: \(v_{1_e} = \sqrt{\frac{GM_e}{R_e}}\) Thus, the ratio of the first cosmic velocity for the planet and Earth is: \(\frac{v_{1_p}}{v_{1_e}} = \frac{\sqrt{\frac{G\cdot(βM_e)}{αR_e}}}{\sqrt{\frac{GM_e}{R_e}}} = \sqrt{\frac{βM_e}{αR_e}\cdot\frac{1}{M_e}\cdot\frac{R_e}{1}} = \sqrt{\frac{β}{α}}\) The second cosmic velocity on Earth is: \(v_{2_e} = \sqrt{\frac{2GM_e}{R_e}}\) Thus, the ratio of the second cosmic velocity for the planet and Earth is: \(\frac{v_{2_p}}{v_{2_e}} = \frac{\sqrt{\frac{2G\cdot(βM_e)}{αR_e}}}{\sqrt{\frac{2GM_e}{R_e}}} = \sqrt{\frac{2\cdotβM_e}{αR_e}\cdot\frac{1}{M_e}\cdot\frac{R_e}{2}} = \sqrt{\frac{β}{α}}\) So the ratios of the acceleration due to gravity and the first and second cosmic velocities for the planet to the corresponding quantities for Earth are: Gravitational acceleration ratio: \(\frac{β}{α^2}\) First cosmic velocity ratio: \(\sqrt{\frac{β}{α}}\) Second cosmic velocity ratio: \(\sqrt{\frac{β}{α}}\)

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Cosmic Velocities
Cosmic velocities are critical speeds to consider when studying celestial bodies and space travel. These include the first cosmic velocity, also known as the orbital velocity, which is the speed needed for an object to enter a stable orbit around a planet without propelling itself. The second cosmic velocity, or escape velocity, is the speed necessary for an object to break free from a planet's gravitational pull.

In our exercise, the comparison between another planet and Earth in terms of these velocities provides insight into how mass and radius influence gravitational forces and the energy required for orbital and escape trajectories.

Understanding these concepts is essential for space exploration, satellite deployment, and comprehending the dynamics of celestial objects in the cosmos.
Classical Mechanics
Classical mechanics is the branch of physics that deals with the motion of objects and the forces that affect them. It is rooted in Newton's laws of motion and the universal law of gravitation. The fundamental premise is that an object will remain at rest or in uniform motion unless acted upon by a force.

The formulas used in our textbook exercise are derived from this field, considering gravitational force as the central force influencing the motion of celestial bodies. These formulas help us calculate how different planets' sizes and masses would affect the force of gravity acting upon them and their cosmic velocities, providing a classical perspective on planetary motion.
Orbital Velocity
Orbital velocity is defined as the speed at which an object must travel to balance gravitational pull and centrifugal force, creating a stable orbit around a planet. It is interesting to note that the orbital velocity is not constant and varies depending on the altitude of the orbit and the mass of the planet.

In the exercise, we explored how changing a planet's size and mass affects its orbital velocity. This understanding is critical for applications such as launching satellites, where precise calculations ensure they maintain their designated orbits without falling back to Earth or drifting into space.
Escape Velocity
Escape velocity is the minimum speed needed for an object to overcome the gravitational pull of a planet and fly into space without further propulsion. This velocity depends on the celestial body's mass and radius. The larger and more massive a planet is, the higher its escape velocity.

The calculation in our exercise showed us how the escape velocity would change if Earth’s dimensions and mass were different. This information is vital for space missions, where spacecraft must reach this velocity to travel to other planets or beyond the solar system.

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Most popular questions from this chapter

Show that if a field is axially symmetric and conservative, then its potential energy has the form \(U=U(r, z)\), where \(r, \varphi\), and \(z\) are cylindrical coordinates. In particular, it follows from this that the vectors of the field lie in planes through the \(z\) axis. As an example of such a field we can take the gravitational field created by a solid of revolution.

The first cosmic velocity is the velocity of motion on a circular orbit of radius close to the radius of the earth. Find the magnitude of the first cosmic velocity \(v_{1}\) and show that \(v_{2}=\sqrt{2} v_{1}\) (cf. Section 3B).

Show that the angle \(\Phi\) between the pericenter and apocenter is equal to the semiperiod of an oscillation in the one-dimensional system with potential energy \(W(x)=U(M / x)+\left(x^{2} / 2\right)\). $$ \Phi=\int_{x_{\min }}^{x_{\max }} \frac{d x}{\sqrt{2(E-W)}} $$

Let \(U(r)=-k r^{-\beta}, 0<\beta<2\). Find \(\Phi_{0}=\lim _{E \rightarrow-0} \Phi\).

Show that the center of mass is well defined, i.e., does not depend on the choice of the origin of reference for radius vectors. The momentum of a system is equal to the momentum of a particle lying at the center of mass of the system and having mass \(\sum m_{i}\). In fact, \(\left(\sum m_{i}\right) \mathbf{r}=\sum\left(m_{i} \mathbf{r}_{i}\right)\), from which it follows that \(\left(\sum m_{i}\right) \dot{\mathbf{r}}=\sum m_{i} \dot{\mathbf{r}}_{i}\). We can now formulate the theorem about momentum as a theorem about the motion of the center of mass.

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