• Support PF! Buy your school textbooks, materials and every day products via PF Here!

Gravitational problems

  • Thread starter nns91
  • Start date
301
0
1. Homework Statement

1. Suppose you leave the solar system and arrive at a planet that has the same mass per unit volume as the earth but has 10 times the earth's radius. What would you weigh on this planet compared with what you weigh on earth ??

2. Suppose that Kepler had found that the period of a planet's circular orbit is proportional to the square of the orbit radius. What conclusion would Newton have drawn concerning the dependence of the gravitational attraction on distance between two masses.

2. Homework Equations

F= -Gm1m2/r^2

3. The Attempt at a Solution

1. So I use Newton's law of gravitational and get you weigh 1/100 (radius is 10, square is 100) as you do on Earth. I am wrong. So how should I approach this problem ?

2. Can you guys hint me how should I do this one ?
 

LowlyPion

Homework Helper
3,079
4
1. Homework Statement

1. Suppose you leave the solar system and arrive at a planet that has the same mass per unit volume as the earth but has 10 times the earth's radius. What would you weigh on this planet compared with what you weigh on earth ??

2. Suppose that Kepler had found that the period of a planet's circular orbit is proportional to the square of the orbit radius. What conclusion would Newton have drawn concerning the dependence of the gravitational attraction on distance between two masses.

2. Homework Equations

F= -Gm1m2/r^2

3. The Attempt at a Solution

1. So I use Newton's law of gravitational and get you weigh 1/100 (radius is 10, square is 100) as you do on Earth. I am wrong. So how should I approach this problem ?

2. Can you guys hint me how should I do this one ?
2 things changed. Radius and what else?
 
301
0
Radius change so mass will change too right ??
 

LowlyPion

Homework Helper
3,079
4
Radius change so mass will change too right ??
Correct.

How does the total mass change with the radius if the density is a constant?

And of course the distance from the center changes directly with the radius.
 
301
0
Mass changes at the same rate as radius does. Right ?
 
301
0
So F= -Gm(10M)/ 100R^2 ??
 

LowlyPion

Homework Helper
3,079
4
So F= -Gm(10M)/ 100R^2 ??
No what is the formula for the mass given the density?

Isn't that Mass = density * volume?
 
301
0
Oh yeah, I misunderstood you.

but how can this help with finding your weight ?
 

LowlyPion

Homework Helper
3,079
4
Oh yeah, I misunderstood you.

but how can this help with finding your weight ?
What is the volume of a sphere again?
 
301
0
V= 4/3*pi*r^3
 

Related Threads for: Gravitational problems

  • Posted
Replies
10
Views
2K
  • Posted
Replies
4
Views
979
  • Posted
Replies
3
Views
910
  • Posted
Replies
3
Views
906
  • Posted
Replies
1
Views
2K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top