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~Gravity on a distant planet

  • Thread starter sam2k2002
  • Start date
10
0
1. Homework Statement
You have been visiting a distant planet. Your measurements have determined that the planet's mass is twice that of earth but the free-fall acceleration at the surface is only one-fourth as large. Radius = 1.8*10^7meters
Mass = 1.19484 × 10^25 kilograms


2. Homework Equations
U_g = -(G*M*m)/r
v_escape = sqrt(2GM/r)

3. The Attempt at a Solution

I just plugged in the variables to the espace velocity equation and get 94km/s, but thats incorrect.
 

Answers and Replies

10
0
The radius was given in the first part of the problem.
 
Dick
Science Advisor
Homework Helper
26,258
618
Um. The radius and the mass are correct. But I get 9.4km/sec. Check the decimal point.
 
Dick
Science Advisor
Homework Helper
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[tex]g_e = \frac{GM_{e}}{R_{e}}[/tex]

[tex]\frac{1}{4}g_e = g_{distant planet}[/tex]

[tex]\frac{1}{4}*\frac{GM_{e}}{R_{e}} = \frac{G*2M_{e}}{R_{distant planet}}[/tex]

[tex]\frac{1}{4*R_{e}} = \frac{2}{R_{distant planet}}[/tex]

[tex]R_{distant planet} = 8R_{e}[/tex]
g=G*M/r^2. It's force/mass not potential/mass.
 
1,341
3
Yeah, looks like I was just being retarded
 
Dick
Science Advisor
Homework Helper
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Yeah, looks like I was just being retarded
S'ok. Reminds me of my post where I was strongly suggesting an OP integrate voltage over a gaussian surface to get enclosed charge. Duh.
 
1,341
3
S'ok. Reminds me of my post where I was strongly suggesting an OP integrate voltage over a gaussian surface to get enclosed charge. Duh.
Lol, guess we all screw up sometimes :rofl:
 

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