Consider a uniform gravitational field (a fair approximation near the surface of a planet). Find

Principles of Physics: A Calculus-Based Text
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ISBN:9781133104261
Author:Raymond A. Serway, John W. Jewett
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Chapter6: Energy Of A System
Section: Chapter Questions
Problem 52P
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Part A
Learning Goal:
To understand the relationship between the force and the potential energy changes
associated with that force and to be able to calculate the changes in potential energy as
definite integrals.
Consider a uniform gravitational field (a fair approximation near the surface of a planet). Find
Imagine that a conservative force field is defined in a certain region of space. Does this
sound too abstract? Well, think of a gravitational field (the one that makes apples fall down
and keeps the planets orbiting) or an electrostatic field existing around any electrically
charged object.
U(y:) – U(yo) = -
where
F =-mg j and ds = dy j.
If a particle is moving in such a field, its change in potential energy does not depend on the
particle's path and is determined only by the particle's initial and final positions. Recall that,
in general, the component of the net force acting on a particle equals the negative
derivative of the potential energy function along the corresponding axis:
Express your answer in terms of m, g, yo, and yf.
• View Available Hint(s)
dU(r)
F,
%3D
dz
?
Therefore, the change in potential energy can be found as the integral
AU = -
U(yt) – U(yo) =
where AU is the change in potential energy for a particle moving from point 1 to point 2,
F is the net force acting on the particle at a given point of its path, and ds is a small
displacement of the particle along its path from 1 to 2.
Submit
Evaluating such an integral in a general case can be a tedious and lengthy task. However,
two circumstances make it easier:
Part B
1. Because the result is path-independent, it is always possible to consider the
most straightforward way to reach point 2 from point 1.
2. The most common real-world fields are rather simply defined.
Consider the force exerted by a spring that obeys Hooke's law. Find
U(xf) – U(xo) = - S F, dš,
where
F, = -ka i, ds = dæ î
In this problem, you will practice calculating the change in potential energy for a particle
moving in three common force fields.
and the spring constant k is positive.
Express your answer in terms of k, xo, and æf.
Note that, in the equations for the forces, i is the unit vector in the x direction, j is the unit
vector in the y direction, and f is the unit vector in the radial direction in case of a
spherically symmetrical force field.
• View Available Hint(s)
?
U(Tt) – U(x0) =
Transcribed Image Text:Part A Learning Goal: To understand the relationship between the force and the potential energy changes associated with that force and to be able to calculate the changes in potential energy as definite integrals. Consider a uniform gravitational field (a fair approximation near the surface of a planet). Find Imagine that a conservative force field is defined in a certain region of space. Does this sound too abstract? Well, think of a gravitational field (the one that makes apples fall down and keeps the planets orbiting) or an electrostatic field existing around any electrically charged object. U(y:) – U(yo) = - where F =-mg j and ds = dy j. If a particle is moving in such a field, its change in potential energy does not depend on the particle's path and is determined only by the particle's initial and final positions. Recall that, in general, the component of the net force acting on a particle equals the negative derivative of the potential energy function along the corresponding axis: Express your answer in terms of m, g, yo, and yf. • View Available Hint(s) dU(r) F, %3D dz ? Therefore, the change in potential energy can be found as the integral AU = - U(yt) – U(yo) = where AU is the change in potential energy for a particle moving from point 1 to point 2, F is the net force acting on the particle at a given point of its path, and ds is a small displacement of the particle along its path from 1 to 2. Submit Evaluating such an integral in a general case can be a tedious and lengthy task. However, two circumstances make it easier: Part B 1. Because the result is path-independent, it is always possible to consider the most straightforward way to reach point 2 from point 1. 2. The most common real-world fields are rather simply defined. Consider the force exerted by a spring that obeys Hooke's law. Find U(xf) – U(xo) = - S F, dš, where F, = -ka i, ds = dæ î In this problem, you will practice calculating the change in potential energy for a particle moving in three common force fields. and the spring constant k is positive. Express your answer in terms of k, xo, and æf. Note that, in the equations for the forces, i is the unit vector in the x direction, j is the unit vector in the y direction, and f is the unit vector in the radial direction in case of a spherically symmetrical force field. • View Available Hint(s) ? U(Tt) – U(x0) =
Part C
Finally, consider the gravitational force generated by a spherically symmetrical massive object. The magnitude and direction of such a force are given by Newton's law of gravity:
Gmim2 î.
where ds = drî; G, mj, and m, are constants; and r>0. Find
U(r¡) – U(ro) = -
F • dš.
Express your answer in terms of G, m1, m2, ro, and rf.
• View Available Hint(s)
Πν ΑΣφ
?
U(r:) – U(ro) =
Submit
Transcribed Image Text:Part C Finally, consider the gravitational force generated by a spherically symmetrical massive object. The magnitude and direction of such a force are given by Newton's law of gravity: Gmim2 î. where ds = drî; G, mj, and m, are constants; and r>0. Find U(r¡) – U(ro) = - F • dš. Express your answer in terms of G, m1, m2, ro, and rf. • View Available Hint(s) Πν ΑΣφ ? U(r:) – U(ro) = Submit
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