Chapter 8: Q18P (page 407)
Find the family of orthogonal trajectories of the circles . (See the instructions above Problem 2.31.)
Short Answer
Answer
The family of orthogonal trajectories of the circles:
Chapter 8: Q18P (page 407)
Find the family of orthogonal trajectories of the circles . (See the instructions above Problem 2.31.)
Answer
The family of orthogonal trajectories of the circles:
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Get started for freeFind the solutions of (1.2)and (1.3), if ( const.).
(a) Show that , and so on; that is, for any positive integral ,
Thus, show that ifis any polynomial in the operator , then .
This is called the exponential shift.
(b) Use to show that .
(c) Replace by , to obtain
This is called the inverse exponential shift.
(d) Using (c), we can change a differential equation whose right-hand side is an exponential times a
polynomial, to one whose right-hand side is just a polynomial. For example, consider
; multiplying both sides by and using (c), we get
Show that a solution of is ; then or use this method to solve Problems 23 to 26.
Find the distance which an object moves in time if it starts from rest and has acceleration. Show that for smallthe result is approximately, and for very large, the speedis approximately constant. The constant is called the terminal speed . (This problem corresponds roughly to the motion of a parachutist.)
Solve the differential equation by changing from variables role="math" localid="1655272385100" to where ; then .
(a)Consider a light beam travelling downward into the ocean. As the beam progresses, it is partially absorbed and its intensity decreases. The rate at which the intensity is decreasing with depth at any point is proportional to the intensity at that depth. The proportionality constant is called the linear absorption coefficient. Show that if the intensity at the surface is , the intensity at a distance s below the surface is . The linear absorption coefficient for water is of the order of (the exact value depending on the wavelength of the light and the impurities in the water). For this value of μ, find the intensity as a fraction of the surface intensity at a depth of 1 ft, ft,
ft,
mile. When the intensity of a light beam has been reduced to half its surface intensity , the distance the light has penetrated into the absorbing substance is called the half-value thickness of the substance. Find the half-value thickness in terms of . Find the half-value thickness for water for the value of given above.
(b) Note that the differential equation and its solution in this problem are mathematically the same as those in Example 1, although the physical problem and the terminology are different. In discussing radioactive decay, we call the decay constant, and we define the half-life T of a radioactive substance as the time when (compare half-value thickness). Find the relation between and T.
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