Understanding the Force of Gravity and Acceleration on a Planet's Surface"

[cary5]

What is the acceleration due to gravity on the surface of a planet with mass 5.00 x 1023 kg and radius 3.00 x 107 m? If you need to, suppose that a block of mass 50 kg is at rest on the surface. Why does it not matter what the mass of the block is?


a= Fnet/mass


i don't know the Fnet

 

[Doc Al]

Hint: Newton's law of gravity.

 

[cary5]

Fg=G*m*m/r sqd
but that does not give me g and besids i need 2 masses for this

 

[Doc Al]

Fg=G*m*m/r sqd
but that does not give me g and besids i need 2 masses for this

You have the mass of the planet--that's all you need. Use the equation from your first post.

 

[cary5]

You have the mass of the planet--that's all you need. Use the equation from your first post.

Fnet/5*1o^23=a ?
now i have 2 varabls

 

[Doc Al]

Fnet/5*1o^23=a ?
now i have 2 varabls

No. Write the force of gravity on some mass m as:

Fg = G*M*m/r^2

where M is the mass of the planet

The acceleration due to gravity is Fg/m.

 

[cary5]

No. Write the force of gravity on some mass m as:

Fg = G*M*m/r^2

where M is the mass of the planet

The acceleration due to gravity is Fg/m.

Fg=(6.67*10^-11)(5.00*10^23)(m)/(3.00*10^7)^2
=0.037m

 

[Doc Al]

Fg=(6.67*10^-11)(5.00*10^23)(m)/(3.00*10^7)^2
=0.037m

Sounds good to me. So what's the acceleration due to gravity?

 

[cary5]

Sounds good to me. So what's the acceleration due to gravity?

0.037m/5.0*10^23
=(7.4*10^-26)m

 

[Doc Al]

0.037m/5.0*10^23
=(7.4*10^-26)m

No. Go back to post #6. a = Fg/m (not Fg/M)

 

[barthayn]

What is the acceleration due to gravity on the surface of a planet with mass 5.00 x 1023 kg and radius 3.00 x 107 m? If you need to, suppose that a block of mass 50 kg is at rest on the surface. Why does it not matter what the mass of the block is?a= Fnet/massi don't know the Fnet

Acceleration due to gravity is the same as the force of gravity for a 1 kg mass. For example, Earth's acceleration due to gravity is 9.8 m/s/s while its force for a one kg mass is 9.8 N. From this you can assume the second mass needed is one kg.

This allows you to use Newton's Universal Law of Gravity to isolate for F_g. If you used the second mass of the object as one, it should be the same for the acceleration due to gravity on that planet.

 

[cary5]

Acceleration due to gravity is the same as the force of gravity for a 1 kg mass. For example, Earth's acceleration due to gravity is 9.8 m/s/s while its force for a one kg mass is 9.8 N. From this you can assume the second mass needed is one kg.

This allows you to use Newton's Universal Law of Gravity to isolate for F_g. If you used the second mass of the object as one, it should be the same for the acceleration due to gravity on that planet.

ya that sounds good and it actuly makes sense