Mechanics Berkeley Physics

Charles Kittel, Walter D. Knight, Malvin A. Ruderman, A. Carl Helmholz, Burton J. Moyer

Chapter 1

Introduction - all with Video Answers

Educators

Chapter Questions

Problem 1

The known unicerse. Using information in the text, estimate the following:
(a) The total mass in the known universe.
(b) The average density of matter in the universe. $A n s-10^{-29} \mathrm{~g} / \mathrm{cm}^{3}$, equivalent to 10 hydrogen atoms $/ \mathrm{m}^{3}$
(c) The ratio of the radius of the known universe to that of a proton. Take the radius of the proton to be $1 \times 10^{-13}$ $\mathrm{cm}$ and the mass of the proton to be $1.7 \times 10^{-24} \mathrm{~g}$.

Ahmed Ali

Ahmed Ali

Numerade Educator

Problem 2

Signals across $a$ proton. Estimate the time required for a signal traveling with the speed of light to move a distance equal to the diameter of a proton. Take the diameter of the proton to be $2 \times 10^{-13} \mathrm{~cm}$. (This time is a convenient reference interval in the physics of elementary particles and nuclei.)

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 3

Distance of Sirius. The parallax of a star is one-half the angle subtended at the star by the extreme points in the earth's orbit around the sun. The parallax of Sirius is $0.371^{\prime \prime}$. Find its distance in centimeters, light years, and parsecs. One parsec is the distance to a star whose parallax is $1^{\prime \prime} .$ (See the table of values inside the front and back covers.)

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 4

Size of atoms. Using the value of Avogadro's number given in the table inside the back cover of the book and your estimate of an average density for common solids, estimate roughly the diameter of an average atom, that is, the dimension of the cubical space filled by the atom.

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 5

Angle subtended by moon. Obtain a millimeter scale and, when viewing conditions are favorable, try the following experiment: Hold the scale at arm's length and measure the diameter of the moon; measure the distance from the scale to your eye. (The radius of the moon's orbit is $3.8 \times 10^{10} \mathrm{~cm}$, and the radius of the moon itself is $1.7 \times 10^{\mathrm{s}} \mathrm{cm}$.)
(a) If you were able to try the measurement, what was the result?
(b) If the measurement could not be made, from the data given above calculate the angle subtended by the moon at the earth. $\quad$ Ans. $9 \times 10^{-3}$ radians $(\mathrm{rad}) .$
(c) What is the angle subtended at the moon by the earth?

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 6

Age of the universe. Assuming the radius of the universe given on page 4 , find the age of the universe from the assumption that a star now on the radius has been traveling outward from the center since the beginning at $0.6 c=1.8 \times$ $10^{10} \mathrm{~cm} / \mathrm{s}(c=$ speed of light in free space).

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 7

Angles in a spherical triangle. Find the sum of the angles in the spherical triangle shown in Fig. $1.5$, assuming $A$ is at the pole and $a=$ radius of sphere. In order to find the angle at $A$, consider what would be the value of $a$ in order for the angle to be $90^{\circ}$.

Thomas Emment

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