How to solve this ratio/proportionality question?

  • Thread starter Tangeton
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In summary, the gravitational pull of the Moon on the Earth's oceans is approximately 3 millionths of the gravitational pull of the Earth on its oceans.
  • #1
Tangeton
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The Moon's gravitational pull on the Earth causes the ocean tides. Show that the gravitational pull of the Moon on the Earth's oceans is approximately 3 millionths of the gravitational pull of the Earth on its oceans. Assume that the distance from the Earth to the Moon is 380,000 km.
Other given/worked out previously: mass of moon = 7.35 x10^22kg, surface gravitational field strength of the moon: 1.62Nkg^-1, radius of the moon = 1740km (3sf)

g at the Earth's surface is 9.8.
g at moon's surface I worked out using the formula g = GM/r^2,g * mass of moon/ distance from moon to Earth sqred = 3.40x10^-5 (3sf)

My big problem is the ratios. How do I show that its 3/1000000 of the grav. pull of the Earth? I know that grav pull of the Earth on oceans will be 9.8 and the moon on the ocean will be 3.40x10^-5, but I just simply do not know how to do physics ratio questions whatsoever. I am terrible at them... How do I approach ratio/ proportionality question such as this one? What is the process?
 
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  • #2
Tangeton said:
The Moon's gravitational pull on the Earth causes the ocean tides. Show that the gravitational pull of the Moon on the Earth's oceans is approximately 3 millionths of the gravitational pull of the Earth on its oceans. Assume that the distance from the Earth to the Moon is 380,000 km.
Other given/worked out previously: mass of moon = 7.35 x10^22kg, surface gravitational field strength of the moon: 1.62Nkg^-1, radius of the moon = 1740km (3sf)

g at the Earth's surface is 9.8.
g at moon's surface I worked out using the formula g = GM/r^2,g * mass of moon/ distance from moon to Earth sqred = 3.40x10^-5 (3sf)

My big problem is the ratios. How do I show that its 3/1000000 of the grav. pull of the Earth? I know that grav pull of the Earth on oceans will be 9.8 and the moon on the ocean will be 3.40x10^-5, but I just simply do not know how to do physics ratio questions whatsoever. I am terrible at them... How do I approach ratio/ proportionality question such as this one? What is the process?
You're nearly there, what do you get if you divide the moon's pull on the ocean, by the Earth's?
 
  • #3
Vagn said:
You're nearly there, what do you get if you divide the moon's pull on the ocean, by the Earth's?
Okay that was too easy. Thanks.
 

1. How do I know if a ratio/proportionality question is solvable?

First, check if the given values are in the same units. If they are, then the question is solvable. If not, try converting them into the same units.

2. What is the difference between a ratio and a proportionality question?

A ratio question compares the relationship between two quantities, while a proportionality question involves finding the constant of proportionality between two quantities.

3. How do I set up and solve a ratio/proportionality question?

To set up a ratio question, write the given values in fraction form and use equivalent fractions to find the unknown value. To solve a proportionality question, set up a proportion using the given values and the constant of proportionality, and then solve for the unknown value using cross multiplication.

4. Can I solve a ratio/proportionality question using other methods?

Yes, there are other methods such as using the unitary method or setting up and solving a system of equations. However, the most commonly used method is setting up and solving a proportion.

5. What are some real-life applications of ratio and proportionality?

Ratios and proportions are used in various fields such as cooking, finance, and science. For example, in cooking, ratios are used to scale recipes depending on the number of servings needed. In finance, proportions are used to calculate interest rates. In science, proportions are used to analyze data and make predictions.

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