- #1
ayloedxa
- 15
- 0
There are two point masses in space, each 1kg and one metre apart from each other.
The only Force acting on the masses is the gravitational force between them.
After what time do they collide?
Gravitational Force F = Gm1m2/(2s)2 where m is the mass and s the distance to the center of both masses (Hence 2s the distance between them). G is the gravitational constant.
F = G*1*1/(2*0.5)2 = G
As F = ma and m is 1, a = G at the initial position.
As the masses don't change I can say for all moments: a(s) = G(2s)-2
The acceleration a is a function of s, the distance, and not time, as usual.
From there on I was stuck.
My guess was that a(s) = dv/ds
And as a(t) = dv/dt = dv/ds*ds/dt and ds/dt = Velocity v
a(t) = a(s)*v
But I have no clue what velocity this is? Is this a totally wrong approach?
Another thought was to take the average acceleration and use it for my calculations.
When s = 0.5m the acceleration is 1G, and when s = 0.25m it is 4G.
Is 4G the average acceleration?
t = √(2s/a) = √(1/4G) = 61221.94s = 17 hours
If this average acceleration is wrong, how do I calculate it?
I would thank you for any help :S
The only Force acting on the masses is the gravitational force between them.
After what time do they collide?
Gravitational Force F = Gm1m2/(2s)2 where m is the mass and s the distance to the center of both masses (Hence 2s the distance between them). G is the gravitational constant.
F = G*1*1/(2*0.5)2 = G
As F = ma and m is 1, a = G at the initial position.
As the masses don't change I can say for all moments: a(s) = G(2s)-2
The acceleration a is a function of s, the distance, and not time, as usual.
From there on I was stuck.
My guess was that a(s) = dv/ds
And as a(t) = dv/dt = dv/ds*ds/dt and ds/dt = Velocity v
a(t) = a(s)*v
But I have no clue what velocity this is? Is this a totally wrong approach?
Another thought was to take the average acceleration and use it for my calculations.
When s = 0.5m the acceleration is 1G, and when s = 0.25m it is 4G.
Is 4G the average acceleration?
t = √(2s/a) = √(1/4G) = 61221.94s = 17 hours
If this average acceleration is wrong, how do I calculate it?
I would thank you for any help :S