2007-01-04 22:58:48 · 7 answers · asked by Ritch 3 in Science & Mathematics ➔ Astronomy & Space
Hmm good question!
To escape a planet's gravitational speed, you have to be travelling at the 'Escape Velocity'. For Earth, the escape velocity is about 39,600 km/h - far more than someone is able to jump!
Say a pro basketballer can jump 2.5m in the air on Earth, that means his velocity when he starts jumping is 23km/hr. So to work out what mass of a planet there has to be to keep him from floating off you have to use the escape velocity equation
0.5 mv^2 = GMm/r
where v is the escape velocity, G is the gravitational constant, M is the mass of the body being escaped from, m is the mass of the basketballer (factors out), and r is the distance between the centre of the body and the point at which escape velocity is being calculated - i.e. the radius of the planet.
2007-01-04 23:10:37 · answer #1 · answered by Robin the Electrocuted 5 · 0⤊ 0⤋
You can't really answer that question within the terms given. The gravitational pull at the surface of a planet is dependent on it's mass and radius. It also depends on what you mean by walk on it. I assume that you mean that the gravity needs to be enough that you can't reach escape velocity by jumping. I'm guessing that I can jump at say an inital 6ms so the mass radius ratio would need to be 18/G or approx 2.7x10^11.
2007-01-04 23:16:30 · answer #2 · answered by Mark G 7 · 0⤊ 0⤋
If you were able to float off because of lack of gravity then there would be no gravity to hold the planet together therefore there would be no planet. Size has nothing to do with `strength` of gravity, mass does, the more mass the greater the gravity.
2007-01-04 23:09:32 · answer #3 · answered by Spanner 6 · 0⤊ 1⤋
As you walk you expend energy.
On a small body as you walk you would float up and down.
If you surpassed the escape velocity then you would float right on out to space.
2007-01-04 23:22:57 · answer #4 · answered by Billy Butthead 7 · 0⤊ 0⤋
You should rephrase it to say how dense does a planet have to be. Mass isn't the only contributor to gravity, density plays a role as well.
2007-01-05 00:44:41 · answer #5 · answered by aorton27 3 · 0⤊ 0⤋
I've heard that you could jump into orbit round Mars's little moons, Phobos and Deimos. I haven't done the calculations to check though.
2007-01-05 00:16:13 · answer #6 · answered by Paul FB 3 · 0⤊ 0⤋
It would have to be about the size of a large asteroid - therefore it could not be classified as a planet.
Hope this answers your question.
2007-01-04 23:16:53 · answer #7 · answered by sneek_matrix 2 · 0⤊ 0⤋