Weight on [Planet] Question

In summary, Neptune has a masss 17.2 times larger than that of Earth and a radius 3.88 times larger. A person weighing 176 lb on the Earth would weigh how much on Neptune? Earth's mass is 6x10^24; Earth's radius is 6.4x10^6. Neptune's mass is 1.032x10^26; Neptune's radius is 24832000. 176 lbs is 80 kgs.
  • #1
davev
31
0
Neptune has a masss 17.2 times larger than that of Earth and a radius 3.88 times larger. A person weighing 176 lb on the Earth would weigh how much on Neptune?

Earth's mass is 6x10^24; Earth's radius is 6.4x10^6. Neptune's mass is 1.032x10^26; Neptune's radius is 24832000. 176 lbs is 80 kgs.




Weight (or Force) = G[itex]\frac{Mplanet\bullet Mperson}{r2}[/itex]

G (universal) = 6.7x10^-11
Mperson for Earth = 80 kgs
Mplanet for Earth = 6x10^24 kgs
r for Earth = 6.4x10^6

Mperson for Neptune = ?
Mplanet for Neptune = 1.032x10^26
r for Neptune = 24832000



Every time I try to solve for the mass of the person on Neptune, I keep getting around 70 kgs, which is 154 lbs. The correct answer according to my online homework system is 201.084048 lbs.

First, I solve for Force on Earth. I plug all four values into the equation to get 785.15625 Newtons.

Second, I then plug the answer above into the Force value to solve for Mperson on Neptune. To isolate Mperson I multiply both sides of the equation by r^2, divide both sides of the equation by G, and divide both sides of the equation by Mplanet. The answer I get is 70.02 kgs, which is 154.05 lbs. That is not the correct answer.


I know that all I really need to do is divide 3.88^2 by 17.2, then multiply that value by 176, but I want to find out what I'm doing wrong. I don't want to use any shortcuts until I actually understand the long process.

Thanks!
 
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  • #2
davev said:
Neptune has a masss 17.2 times larger than that of Earth and a radius 3.88 times larger. A person weighing 176 lb on the Earth would weigh how much on Neptune?

Earth's mass is 6x10^24; Earth's radius is 6.4x10^6. Neptune's mass is 1.032x10^26; Neptune's radius is 24832000. 176 lbs is 80 kgs.

Weight (or Force) = G[itex]\frac{Mplanet\bullet Mperson}{r2}[/itex]

G (universal) = 6.7x10^-11
Mperson for Earth = 80 kgs
Mplanet for Earth = 6x10^24 kgs
r for Earth = 6.4x10^6

Mperson for Neptune = ?
Mplanet for Neptune = 1.032x10^26
r for Neptune = 24832000
Every time I try to solve for the mass of the person on Neptune, I keep getting around 70 kgs, which is 154 lbs. The correct answer according to my online homework system is 201.084048 lbs.

First, I solve for Force on Earth. I plug all four values into the equation to get 785.15625 Newtons.

Second, I then plug the answer above into the Force value to solve for Mperson on Neptune. To isolate Mperson I multiply both sides of the equation by r^2, divide both sides of the equation by G, and divide both sides of the equation by Mplanet. The answer I get is 70.02 kgs, which is 154.05 lbs. That is not the correct answer.


I know that all I really need to do is divide 3.88^2 by 17.2, then multiply that value by 176, but I want to find out what I'm doing wrong. I don't want to use any shortcuts until I actually understand the long process.

Thanks!

You are going the long way around. Mperson on Earth=Mperson on Neptune and it's about 80kg. You don't need to solve for a different mass on Neptune. Mass doesn't change. Only the weight changes.
 
Last edited:
  • #3
Dick said:
You are going the long way around. Mperson on Earth=Mperson on Neptune and it's about 80kg. You don't need to solve for a different mass on Neptune. Mass doesn't change. Only the weight changes.

Okay, I see what you're saying. I made a note in my notebook regarding universality of mass too, haha. I can't believe I skipped past that.

So if I plug the value for Mplanet of Neptune, Mperson, r^2 of Neptune, and G, then I will get around 897.06 N. I just convert this into pounds right?
 
  • #4
davev said:
Okay, I see what you're saying. I made a note in my notebook regarding universality of mass too, haha. I can't believe I skipped past that.

So if I plug the value for Mplanet of Neptune, Mperson, r^2 of Neptune, and G, then I will get around 897.06 N. I just convert this into pounds right?

Sure, but as you said, just using ratios is the easy way to do it.
 
  • #5
Dick said:
Sure, but as you said, just using ratios is the easy way to do it.

Thank you!
 

What is the weight on [Planet]?

The weight on a planet is determined by its mass and the gravitational pull at the surface. The formula for calculating weight is W=mg, where W is weight, m is mass, and g is the gravitational acceleration. The weight will be different on each planet due to varying gravitational pull.

How does weight differ on [Planet] compared to Earth?

Weight on different planets will differ due to the varying gravitational pull. For example, on Mars, the gravitational pull is about 38% of Earth's, so a person who weighs 100 pounds on Earth would weigh about 38 pounds on Mars. However, their mass would remain the same.

What factors affect weight on [Planet]?

The main factor that affects weight on a planet is the gravitational pull. Other factors may include the planet's mass and radius. The farther away a planet is from a massive object, like a star, the weaker the gravitational pull will be.

Can weight on [Planet] be measured using a scale?

Yes, weight on a planet can be measured using a scale. However, the scale must be calibrated to account for the gravitational pull and mass of the planet. For example, a scale that is calibrated for Earth's gravity would not give an accurate reading on a planet with a different gravitational pull.

Is weight the same as mass?

No, weight and mass are not the same. Weight is a measure of the force of gravity on an object, while mass is a measure of the amount of matter in an object. Mass will remain constant regardless of location, but weight can vary depending on the gravitational pull. On Earth, weight is often used interchangeably with mass due to the consistent gravitational pull, but on other planets, there is a clear distinction between the two.

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