The problem asks us to find the mass $m$ and the center of mass $(\bar{x}, \bar{y})$ of the lamina bounded by the curves $x=0$, $x=4$, $y=0$, $y=3$ with the density function $\delta(x,y) = y+1$.

Applied MathematicsCalculusDouble IntegralsCenter of MassDensity Function
2025/5/25

1. Problem Description

The problem asks us to find the mass mm and the center of mass (xˉ,yˉ)(\bar{x}, \bar{y}) of the lamina bounded by the curves x=0x=0, x=4x=4, y=0y=0, y=3y=3 with the density function δ(x,y)=y+1\delta(x,y) = y+1.

2. Solution Steps

First, we calculate the mass mm:
m=Rδ(x,y)dA m = \int\int_R \delta(x,y) dA
where RR is the region bounded by the given curves.
In this case, RR is the rectangle defined by 0x40 \le x \le 4 and 0y30 \le y \le 3.
Thus,
m=0403(y+1)dydx=04[12y2+y]03dx=04(92+3)dx=04152dx=152[x]04=152(4)=30 m = \int_0^4 \int_0^3 (y+1) dy dx = \int_0^4 [\frac{1}{2}y^2 + y]_0^3 dx = \int_0^4 (\frac{9}{2} + 3) dx = \int_0^4 \frac{15}{2} dx = \frac{15}{2} [x]_0^4 = \frac{15}{2}(4) = 30
Next, we calculate the moments MxM_x and MyM_y:
Mx=Ryδ(x,y)dA M_x = \int\int_R y \delta(x,y) dA
My=Rxδ(x,y)dA M_y = \int\int_R x \delta(x,y) dA
So,
Mx=0403y(y+1)dydx=0403(y2+y)dydx=04[13y3+12y2]03dx=04(273+92)dx=04(9+92)dx=04272dx=272[x]04=272(4)=54 M_x = \int_0^4 \int_0^3 y(y+1) dy dx = \int_0^4 \int_0^3 (y^2+y) dy dx = \int_0^4 [\frac{1}{3}y^3 + \frac{1}{2}y^2]_0^3 dx = \int_0^4 (\frac{27}{3} + \frac{9}{2}) dx = \int_0^4 (9 + \frac{9}{2}) dx = \int_0^4 \frac{27}{2} dx = \frac{27}{2} [x]_0^4 = \frac{27}{2}(4) = 54
My=0403x(y+1)dydx=04x03(y+1)dydx=04x[12y2+y]03dx=04x(92+3)dx=04x(152)dx=15204xdx=152[12x2]04=152(162)=152(8)=60 M_y = \int_0^4 \int_0^3 x(y+1) dy dx = \int_0^4 x \int_0^3 (y+1) dy dx = \int_0^4 x [\frac{1}{2}y^2 + y]_0^3 dx = \int_0^4 x (\frac{9}{2} + 3) dx = \int_0^4 x (\frac{15}{2}) dx = \frac{15}{2} \int_0^4 x dx = \frac{15}{2} [\frac{1}{2}x^2]_0^4 = \frac{15}{2} (\frac{16}{2}) = \frac{15}{2}(8) = 60
Finally, we calculate the coordinates of the center of mass (xˉ,yˉ)(\bar{x}, \bar{y}):
xˉ=Mym=6030=2 \bar{x} = \frac{M_y}{m} = \frac{60}{30} = 2
yˉ=Mxm=5430=95=1.8 \bar{y} = \frac{M_x}{m} = \frac{54}{30} = \frac{9}{5} = 1.8

3. Final Answer

m=30m = 30
xˉ=2\bar{x} = 2
yˉ=95\bar{y} = \frac{9}{5}
The mass is 3030 and the center of mass is (2,95)(2, \frac{9}{5}).

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