# Physic Question

[SOLVED] Physic Question

## Homework Statement

Calculate the location of the center of mass of the Earth-Moon-Sun system during a full Moon. A full Moon occurs when the Earth, Moon, and Sun are lined up as shown in the figure. Use a coordinate system in which the center of the sun is at x=0 and the Earth and Moon both lie along the positive x direction.

The mass of the Moon is 7.35×10^22 kg, the mass of the Earth is 6.00×10^24 kg, and the mass of the sun is 2.00×10^30 kg. The distance between the Moon and the Earth is 3.80×10^5 km. The distance between the Earth and the Sun is 1.50×10^8 km.

## Homework Equations

I am using the x(cm) = m1x1 + m2x2 + m3x3/ m1 + m2 + m3

Where m is masses of the objects and x is distance

## The Attempt at a Solution

I put in x(cm) = ((2.00 x 10^30)(1.50×10^8 km) + (7.35×10^22 kg)(3.80×10^5 km) + (6.00×10^24 kg)(1.50×10^8 km))/(7.35×10^22 kg + 6.00×10^24 kg + 2.00×10^30 kg)

I know I am subbing in the wrong value somewhere.

Last edited:

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x(cm) = m1x1 + m2x2 + m3x3/ m1 + m2 + m3
If you put x1,x2,x3 in Km (as given in the question) then you will get x in Km not cm

Doc Al
Mentor

## Homework Equations

I am using the x(cm) = m1x1 + m2x2 + m3x3/ m1 + m2 + m3
Nothing wrong with this formula.
I am completely stumped. Like i try to sub the values into the equation but I get a huge number and it doesnt seem right
Show exactly what values you plugged in.

Doc Al
Mentor
If you put x1,x2,x3 in Km (as given in the question) then you will get x in Km not cm
In this context, "cm" stands for center of mass (not centimeters).

Nothing wrong with this formula.

Show exactly what values you plugged in.
I put in x(cm) = ((2.00 x 10^30)(1.50×10^8 km) + (7.35×10^22 kg)(3.80×10^5 km) + (6.00×10^24 kg)(1.50×10^8 km))/(7.35×10^22 kg + 6.00×10^24 kg + 2.00×10^30 kg)

Doc Al
Mentor
I put in x(cm) = ((2.00 x 10^30)(1.50×10^8 km) + (7.35×10^22 kg)(3.80×10^5 km) + (6.00×10^24 kg)(1.50×10^8 km))/(7.35×10^22 kg + 6.00×10^24 kg + 2.00×10^30 kg)
Measure all positions with respect to the sun, which is at x = 0. What's the distance of each body from the sun?

(I failed to notice that you gave these details in your first post. D'oh!)

Thanks for the help I got it :) Its just

x(cm) = ((2.00 x 10^30)(0) + (7.35×10^22 kg)(3.80×10^5 km + 1.5x10^8) + (6.00×10^24 kg)(1.50×10^8 km))/(7.35×10^22 kg + 6.00×10^24 kg + 2.00×10^30 kg)