# Graviatational force field

1. Aug 28, 2009

### Allandra

1. The problem statement, all variables and given/known data

By considering the centripetal force acting on a man, calculate the minimum period of rotation that the Earth would need to have about its axis if a man at the equator were to experience zero normal contact force.

2. The attempt at a solution
this means the g=Fc(centripetral force)
to find v= square root of ( radius of the Earth and g)
g=9.81 N/kg and then sub it to T= (2pie x radius of Earth )/v
Where is the error? Does a zero normal force means the person is experiencing weightlessness due to a=g?

2. Aug 28, 2009

### Staff: Mentor

OK, but you mean mg = Fc.
I don't see any error. What your final expression for T?
Yes, that's what "weightlessness" means.

3. Aug 29, 2009

### Allandra

. where radius of the Earth is 6400km
But I can't get the ans=1.41hrs
I can only get 84.3hrs
square root of{Rg}=square root of (6400km X 35.3km/h)= 475
(R multiply by 2pie)divide by T= 40212/T
cross multiply them and I get 84.3hrs. Do u know where is the error?

4. Aug 29, 2009

### Staff: Mentor

When you converted g from m/s^2 to km/h^2, you made an error.

Instead, use standard units: meters and seconds, not km and hours. g = 9.8 m/s^2

When you find the answer in seconds, then convert to hours.

Last edited: Aug 29, 2009
5. Aug 29, 2009

Thx Doc Al!