kinetic energy at an infinite distance away (1 Viewer)

[skillstriker]

why is the kinetic energy of an object an infinite distance away from earth 0?

 

[pdang]

did you mean gravitational potential energy? because otherwise i have never heard of this

 

[skillstriker]

When you're deriving the equation for escape velocity you use law of conservation of energy:
E(initial) = E(final)
GPE + KE = GPE + KE
-GmM/r + 1/2mv^2 = 0 + 0 (--> this is where I'm confused --> why is KE at infinity 0?)

 

[pdang]

oh ok so for escape velocity if you were to throw an object away from a planet at escape velocity, it would break free from the gravitational attraction. This implies that it would never come back down. It keeps going until it reaches the "peak" of its motion where it final velocity is 0, similar to at the peak of a parabolic trajectory.

 

[someth1ng]

It doesn't really "break free" from gravitational attraction. It's always being attracted so it doesn't "break free". Escape velocity just means that that your kinetic energy is matches gravitational potential energy and hence, when you're moving away, you gain potential energy and decrease in kinetic energy but you can only decrease kinetic energy till it's 0 (which occurs at infinity). At that point, you'll have 0 KE and 0 GPE assuming you escaped with a velocity equal to the escape velocity.