# Need help with High School Physics PLEASE!

1. Mar 31, 2008

### starvinmarvin

Hey everyone. I’m in high school Physics and I need some help. We are in a unit involving gravity, mass, and radius and heights of Earth. Here are some equations and givens we have to help:

M1g= (Gm1m2)/r^2
G= 6.67 x 10^-11
R= 6.38 x 10^6
V= Square root of (Gmp/r)
T= Square root of (4pi^2r^3/Gmp)

Any help would be much included. I have tried working on these problems for like 45 minutes already and I can't come up with anything because I don't really even know how to start or continue on these! Please try to include work with your help. THANK YOU!

#7: Calculate the period of Earth’s rotation and its velocity for people at the equator to feel weightless. (Hint: what would FN be?) How long would an Earth day be then? What type of adjustments would we have to make to live in such a situation?

-Fg= -Fc
-mpg= (4pi^2mpr)/T^2 on eartch

#9: At what height above Earth’s surface is gravity half of what it is on the Earth’s surface?

#11: What is the gravitational field strength of a 5.00N object at a distance h above Earth with a mass of 1.34kg? What is the weight of another object at this same height if its mass is 188kg? What is the weight on each kg of mass at this height? What is the gravitational acceleration at this height? What is a force field? Draw the relative gravitational field strength for both objects at h and at a distance of 2h and 1/2h with arrows.

#13: Calculate the height above Mercury that an astronaut would have to be so that her weight would be half that on Mercury? (Hint: r= 2.44 x 10^6)

Last edited: Mar 31, 2008
2. Mar 31, 2008

### YellowTaxi

for #9 all you need is: F = GMm/r^2

If you want F to become half then you need to make the number r^2 go to twice it's original value. (so that all of GMm/r^2 will go to half its original value)

So you would have to make r change to 1.4142 times the initial value [ 1.4142 is the square root of 2]

On earths surface r= 6.38 x 10^6m
so you just need to change that to 1.4142 x 6.38 x 10^6m
F will drop to half.

sorry I didn't understand the facts & figures that you gave, but if you can see how #9 is so easy to solve, that alone might help you work out the other problems as well.