Book: Physics 7th edition, Author: Giancoli Modified 45 the intensity of an eart
ID: 1660652 • Letter: B
Question
Book: Physics 7th edition, Author: Giancoli
Modified 45 the intensity of an earthquake wave passing through the Earth is measured to be 3.0 * 106 J m2 Modify Equation 11-16a for a HEMISPHERICAL wave, as this earthquake approximately
is. That is, assume it spreads out over the area of a HALF sphere. The book has
the wrong units for intensity. It should be watts per square meter, not Joules per square meter.
A) Use this (and the fact that 54.0km is 5.40E4m) to find the power (watts or J/s) of this
earthquake.
B) Find the intensity 10.0km from the source
as the book says. Remember, intensity is
power/area, and your answer should be smaller than the book’s by a factor of 10-squared because
of the inverse r^2
C) Finally, find the power through the area of a square 5.00m on a side
Explanation / Answer
A) Power P = IA
= 3000000 * 4piR2
= 3000000* 2pi * (5.40E4)2
= 5.5 x 1016 W
B) Here R = 10km = 10,000m
I = P/A
= (5.5 x 1017)/2pi*10,0002
= 8.75 x 107 W/m2
C) P = IA
A = side2 = 52 = 25m2
I is not mentioned. Assuming it to be as given in the original question:
I = 3000000 w/m^2
P = 3000000 w/m^2 *25m2
= 7.5 x 107 W