We are asked to analyze the iterated integral $\int_0^2 \int_0^x k \, dy \, dx$. The goal is to sketch the lamina $R$, determine the density $\delta$, and find the mass and center of mass.

AnalysisDouble IntegralsCenter of MassDensityIterated IntegralsCalculusMultivariable Calculus
2025/5/25

1. Problem Description

We are asked to analyze the iterated integral 020xkdydx\int_0^2 \int_0^x k \, dy \, dx. The goal is to sketch the lamina RR, determine the density δ\delta, and find the mass and center of mass.

2. Solution Steps

The iterated integral 020xkdydx\int_0^2 \int_0^x k \, dy \, dx represents a double integral over a region RR in the xyxy-plane.
First, we need to identify the region of integration.
The limits of integration for yy are 0yx0 \le y \le x.
The limits of integration for xx are 0x20 \le x \le 2.
This describes the region bounded by the lines y=0y=0, y=xy=x, and x=2x=2. This is a triangle with vertices at (0,0)(0,0), (2,0)(2,0), and (2,2)(2,2).
The density δ\delta is given by the integrand, which is kk. Since kk is a constant, the density is constant.
The mass MM is given by the double integral:
M=020xkdydx=k020xdydx=k02[y]0xdx=k02xdx=k[12x2]02=k(12(22)0)=2kM = \int_0^2 \int_0^x k \, dy \, dx = k \int_0^2 \int_0^x dy \, dx = k \int_0^2 [y]_0^x dx = k \int_0^2 x \, dx = k \left[ \frac{1}{2}x^2 \right]_0^2 = k \left( \frac{1}{2}(2^2) - 0 \right) = 2k.
The xx-coordinate of the center of mass, xˉ\bar{x}, is given by
xˉ=1M020xxkdydx=12k02xk0xdydx=1202x[y]0xdx=1202x2dx=12[13x3]02=12(83)=43\bar{x} = \frac{1}{M} \int_0^2 \int_0^x xk \, dy \, dx = \frac{1}{2k} \int_0^2 xk \int_0^x dy \, dx = \frac{1}{2} \int_0^2 x \left[ y \right]_0^x dx = \frac{1}{2} \int_0^2 x^2 \, dx = \frac{1}{2} \left[ \frac{1}{3}x^3 \right]_0^2 = \frac{1}{2} \left( \frac{8}{3} \right) = \frac{4}{3}.
The yy-coordinate of the center of mass, yˉ\bar{y}, is given by
yˉ=1M020xykdydx=12k02k0xydydx=1202[12y2]0xdx=120212x2dx=1402x2dx=14[13x3]02=14(83)=23\bar{y} = \frac{1}{M} \int_0^2 \int_0^x yk \, dy \, dx = \frac{1}{2k} \int_0^2 k \int_0^x y \, dy \, dx = \frac{1}{2} \int_0^2 \left[ \frac{1}{2}y^2 \right]_0^x dx = \frac{1}{2} \int_0^2 \frac{1}{2}x^2 \, dx = \frac{1}{4} \int_0^2 x^2 \, dx = \frac{1}{4} \left[ \frac{1}{3}x^3 \right]_0^2 = \frac{1}{4} \left( \frac{8}{3} \right) = \frac{2}{3}.

3. Final Answer

The lamina R is a triangle with vertices (0,0)(0,0), (2,0)(2,0), and (2,2)(2,2).
The density is δ=k\delta = k.
The mass is M=2kM = 2k.
The center of mass is (xˉ,yˉ)=(43,23)(\bar{x}, \bar{y}) = \left( \frac{4}{3}, \frac{2}{3} \right).

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