Universal Gravitation and mass

[Chutzpah]

Homework Statement

mass of star = 2.53 x 1030 kilograms
mass of planet = 5.25 x 1024 kilograms
mass of moon = 8.09 x 1022 kilograms
average distance from star to planet = 1.14 x 1011 meters
average distance from planet to moon = 4.59 x 108 meters

Use the data above to determine the net force exerted on the moon by the planet and the star during:
a. a solar eclipse.
WebAssign will check your answer for the correct number of significant figures. wrong check mark N
b. a lunar eclipse.
WebAssign will check your answer for the correct number of significant figures. wrong check mark N

Homework Equations

Fg=G x M1 x M2/Dsquared
Note that the lineup for a solar eclipse is Sun-Moon-Earth
A lunar eclipse lineup is Sun-Earth-Moon
This I am sure of.

The Attempt at a Solution

My attempt was to find the netforce of gravity on the moon.
Here is my work which produced a wrong answer.
a) Fgrav,net=Gm(moon)M(sun)/Dsquared(the distance between the star and the planet- the distance between the planet and the moon) - GM(moon)M(earth)/dsquared
Perhaps I added the distances wrong- but I know when the moon is in the middle I will have opposite signs for the forces from each planet and the lunar eclipse should produce. I got 9.18E20 rounded for my answer to part a. Any ideas? Am i using the distance wrong? Any similar answers? Any other forces to be accounted for in the net sum? Thanks.

 

[berkeman]

It looks like you are using the correct approach. Can you write out your math steps to make it easier to check them?

 

[m2003]

Thank you for your question. Your attempt at finding the net force of gravity on the moon is correct, but there are a few things that may have led to your incorrect answer. First, make sure you are using the correct values for the masses and distances. The masses given in the homework statement are in kilograms, but the values you used in your attempt (2.53 x 10^30 and 5.25 x 10^24) are in grams. Make sure to convert these values to kilograms before using them in your equation.

Secondly, it seems like you may have used the wrong distances in your calculation. For a solar eclipse, the correct distance to use is the distance between the star and the planet (1.14 x 10^11 meters), and for a lunar eclipse, the correct distance is the distance between the planet and the moon (4.59 x 10^8 meters). Make sure to use the correct distances for each scenario.

Lastly, there may be other forces at play in these scenarios, such as the gravitational force between the moon and the planet or the moon and the Earth. However, these forces would be much smaller compared to the force exerted by the star, so they can be neglected in this calculation.

In summary, to find the net force of gravity on the moon during a solar or lunar eclipse, use the correct values for masses and distances, and make sure to account for the correct distances in each scenario. I hope this helps clarify your understanding of universal gravitation. Keep up the good work!