Chapter 13: Problem 23
Find the center of mass of the following plane regions with variable density. Describe the distribution of mass in the region. The triangular plate in the first quadrant bounded by \(x+y=4\) with \(\rho(x, y)=1+x+y\)
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Chapter 13: Problem 23
Find the center of mass of the following plane regions with variable density. Describe the distribution of mass in the region. The triangular plate in the first quadrant bounded by \(x+y=4\) with \(\rho(x, y)=1+x+y\)
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In Section 10.3 it was shown that the area of a region enclosed by the polar curve \(r=g(\theta)\) and the rays \(\theta=\alpha\) and \(\theta=\beta,\) where \(\beta-\alpha \leq 2 \pi,\) is \(A=\frac{1}{2} \int_{\alpha}^{\beta} r^{2} d \theta .\) Prove this result using the area formula with double integrals.
Explain why or why not ,Determine whether the following statements are true and give an explanation or counterexample. a. A thin plate of constant density that is symmetric about the \(x\) -axis has a center of mass with an \(x\) -coordinate of zero. b. A thin plate of constant density that is symmetric about both the \(x\) -axis and the \(y\) -axis has its center of mass at the origin. c. The center of mass of a thin plate must lie on the plate. d. The center of mass of a connected solid region (all in one piece) must lie within the region.
Gravitational field due to spherical shell A point mass \(m\) is a distance \(d\)
from the center of a thin spherical shell of mass \(M\) and radius \(R .\) The
magnitude of the gravitational force on the point mass is given by the
integral
$$F(d)=\frac{G M m}{4 \pi} \int_{0}^{2 \pi} \int_{0}^{\pi} \frac{(d-R \cos
\varphi) \sin \varphi}{\left(R^{2}+d^{2}-2 R d \cos \varphi\right)^{3 / 2}} d
\varphi d \theta$$
where \(G\) is the gravitational constant.
a. Use the change of variable \(x=\cos \varphi\) to evaluate the integral and
show that if \(d>R,\) then \(F(d)=\frac{G M m}{d^{2}},\) which means the force is
the same as if the mass of the shell were concentrated
at its center.
b. Show that if \(d
Let \(D\) be the solid bounded by the ellipsoid \(x^{2} / a^{2}+y^{2} / b^{2}+z^{2} / c^{2}=1,\) where \(a>0, b>0,\) and \(c>0\) are real numbers. Let \(T\) be the transformation \(x=\)au, \(y=b v, z=c w\) Evaluate \(\iiint_{D}|x y z| d A\)
Water in a gas tank Before a gasoline-powered engine is started, water must be drained from the bottom of the fuel tank. Suppose the tank is a right circular cylinder on its side with a length of \(2 \mathrm{ft}\) and a radius of 1 ft. If the water level is 6 in above the lowest part of the tank, determine how much water must be drained from the tank.
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