Force of Gravity: Mass Change Factors

[cary5]

By what factor does the force change if
a. The mass of the 10-kg ball is doubled?
b. The mass of each ball is doubled?

Fg=(Gm1m2)/r sqrd

i know i can find the anser by using this but i don't know hoe to do it
for (a) i don't have the masse of the second obj.
so double of 10 is 20
Fg=(Gm1*20)/r sqrd but that is not the factor of change

 

[berkeman]

By what factor does the force change if
a. The mass of the 10-kg ball is doubled?
b. The mass of each ball is doubled?

Fg=(Gm1m2)/r sqrd

i know i can find the anser by using this but i don't know hoe to do it
for (a) i don't have the masse of the second obj.
so double of 10 is 20
Fg=(Gm1*20)/r sqrd but that is not the factor of change

They are looking for a ratio of forces, so divide the new force equation by the old one (lots of stuff cancels out...)

 

[cary5]

They are looking for a ratio of forces, so divide the new force equation by the old one (lots of stuff cancels out...)

but there is only one object i can't use the equation with only one mass

 

[berkeman]

but there is only one object i can't use the equation with only one mass

One object? Then why do they ask what happens if the mass of "each" is doubled?

You didn't post the full question, so it's hard to be sure. But looking at what you posted, it looks like the question is about 2 masses, m1 and m2. They are asking what happens to the gravitational attraction force for parts a) and b), no?

 

[cary5]

One object? Then why do they ask what happens if the mass of "each" is doubled?

You didn't post the full question, so it's hard to be sure. But looking at what you posted, it looks like the question is about 2 masses, m1 and m2. They are asking what happens to the gravitational attraction force for parts a) and b), no?

i don't know this the whole question
i give up

 

[berkeman]

i don't know this the whole question
i give up

Why don't you post the whole original question, word for word, before giving up...

 

[cary5]

Why don't you post the whole original question, word for word, before giving up...

that is the whole question but befot that that is another question i think that it is referring to it

Q) What is the force of gravity
a. of a 10-kg steel ball on a 5-kg steel ball if the centers of the balls are 5 meters apart?
b. of a 5-kg steel ball on a 10-kg steel ball if the centers of the balls are 5 meters apart?
c. What is the acceleration of the 10-kg ball?
d. What is the acceleration of the 5-kg ball?

Q)By what factor does the force change if
a. The mass of the 10-kg ball is doubled?
b. The mass of each ball is doubled?

igot everything for the first question the forses on the balls are 1.3*10^-10
so if the force befor was that the new Fg would be 2.7*10^-10 sine the mass of the 10 kg ball is doubled
but it is still not the factor og chage how do i get that is is by dividing them?

 

[berkeman]

that is the whole question but befot that that is another question i think that it is referring to it

Q) What is the force of gravity
a. of a 10-kg steel ball on a 5-kg steel ball if the centers of the balls are 5 meters apart?
b. of a 5-kg steel ball on a 10-kg steel ball if the centers of the balls are 5 meters apart?
c. What is the acceleration of the 10-kg ball?
d. What is the acceleration of the 5-kg ball?

Q)By what factor does the force change if
a. The mass of the 10-kg ball is doubled?
b. The mass of each ball is doubled?

igot everything for the first question the forses on the balls are 1.3*10^-10
so if the force befor was that the new Fg would be 2.7*10^-10 sine the mass of the 10 kg ball is doubled
but it is still not the factor og chage how do i get that is is by dividing them?

They ask by what factor the force changes. So the change is F2/F1, where F2 if the force after making the change in the mass(es).

You already wrote the equation for the gravitational attractive force:

F = G \frac{m_1 m_2}{r^2}

You don't even need to plug in numbers to answer these two questions. For the first question, m1 doubles to 2*m1. For the second question, both m1 and m2 double to 2*m1 and 2*m2. Write the force ratio equation, and plug in the new mass multipliers as appropriate...

 

[cary5]

They ask by what factor the force changes. So the change is F2/F1, where F2 if the force after making the change in the mass(es).

You already wrote the equation for the gravitational attractive force:

F = G \frac{m_1 m_2}{r^2}

You don't even need to plug in numbers to answer these two questions. For the first question, m1 doubles to 2*m1. For the second question, both m1 and m2 double to 2*m1 and 2*m2. Write the force ratio equation, and plug in the new mass multipliers as appropriate...

F2/F1 gives me 2.07 for the firs one
anf for b i got 4.07

 

[berkeman]

F2/F1 gives me 2.07 for the firs one
anf for b i got 4.07

2/1 = 2.07?

4/1 = 4.07?

Other than that, I think you are getting there!

 

[cary5]

2/1 = 2.07?

4/1 = 4.07?

Other than that, I think you are getting there!

u said to do the force of gravity for the doubled mass/ force of gravity for the orignal
(2.7*10^-10)/(1.3*10^-10)=2.07

 

[berkeman]

u said to do the force of gravity for the doubled mass/ force of gravity for the orignal
(2.7*10^-10)/(1.3*10^-10)=2.07

I also said to do it symbollically instead of plugging in bunch of numbers (and making small errors as a result of rounding during the calculations). You can see how your answers are slightly off of the real answers...

 

[cary5]

I also said to do it symbollically instead of plugging in bunch of numbers (and making small errors as a result of rounding during the calculations). You can see how your answers are slightly off of the real answers...

(Gm1*2m)/r squd
i don't know were to go from here

 

[cary5]

I also said to do it symbollically instead of plugging in bunch of numbers (and making small errors as a result of rounding during the calculations). You can see how your answers are slightly off of the real answers...

i think i got it
ok so (gm2m)/r2 divided bt (Gmm)/r2
and now everythig cansles out and we are left with 2m/m and the m's cancle and we get 2/1
is that right? is the facto 2/1 for the firs one

 

[oo7 - 2oo]

it was so easy

F= Gm1m2 / r^2

F`=G10.m1m2 / r^2

cancel the repeting things

 

[berkeman]

i think i got it
ok so (gm2m)/r2 divided bt (Gmm)/r2
and now everythig cansles out and we are left with 2m/m and the m's cancle and we get 2/1
is that right? is the facto 2/1 for the firs one

Yes. Good!

 

[berkeman]

it was so easy

f= gm1m2 / r^2

f`=g10.m1m2 / r^2

cancel the repeting things

g10?