What's the difference between the formula of [math]g = \frac{F_g}{m}[/math] and [math]abs(g) = G\frac{m}{r^2}[/math]?

 

Note: abs(g) means absolute value. I don't know the latex code to input absolute.

 

Because the question asked me: Calculate the gravitational field intensity 340 km above the planet Venus.

 

I used the second formula above, where r = 340,000 m; G = 6.67 x 10^-11; m = 4.83 x 10^24 kg. I got [math]2786.859862 \frac{N}{kg}[/math] for the answer. Is this correct?

 

I still don't know why I used the second formula, not the first one, though?

They're the same thing.

 

[math]\mathbf{g}=\frac{\mathbf{F}}{m}[/math]

 

The force is just

 

[math]G\frac{mM}{r^2}\hat{\mathbf{r}}[/math]

 

To get the absolute value just whack | around the things your taking abs of, there should just be a key on your keyboard for it.

All right thanks.

Because the question asked me: Calculate the gravitational field intensity 340 km above the planet Venus.

 

I used the second formula above' date=' where r = 340,000 m; [/quote']

 

 

Just a query, but r is the distance from the centre of the mass NOT the surface... so is that what they mean by "above the planet"???

Just a query, but r is the distance from the centre of the mass NOT the surface... so is that what they mean by "above the planet"???

 

Yup, I just noticed that in my textbook. I have to find the distance that runs toward the Venus's centre, and add it to the distance "above the surface".

 

Thanks.