Physics
posted by Sarah .
A at disk of material has the same mass as the Earth, 5.98E+24 kg, and has a radius of 6.25 E+07 m. Point A is
located a distance of 5.8E+06 m above the center of the disk. Point B is located right at the center of the disk. Treat all of the mass as if it were located in the xy plane.
An object of mass 250 kg is located near the disk.
a. Find the gravitational potential energy (J) when the object is at point A.
b. Find the gravitational potential energy (J) when the object is at point B.
Answers:
a)2.88E+09 (I keep getting 1.59 E+09)
b)3.19E+09 (I can kinda get this)
I used the Following
a) (GMm)/x, where I used pythagorean and them to get x based on radius and height
b) (Gmm)/r and I used (the r given/2)
that seems to work
I am really confused on what I am doing wrong on part A and if any suggetions on how to correct part B so i don't have to fudge it would be wonderful

The formula you are using for potential energy applies to a spherical object, not a disc.
See http://www.physicsforums.com/showthread.php?t=449947
for the appropriate formula 
So I get most of what the website is saying however, it says M squared, but I have two masses
and only one radius, so I am still a little confused. Please help 
As I recall from that link, the gravitational PE for a point above a disc involves both the distance to the center of the disc and the distance to the edge of the disc.
In both cases, the point must be at or above the center of the disc. That is true in your case. 
Right and I have two different masses that need to be multiplied. The my r0 is 6.25 E 7, and R is 5.8 E 6, but using these number i am still getting 1.48 E 9 and not 2.88 E 9, so I am not sure, I have tried it different ways, am I missing something obvious here?
Respond to this Question
Similar Questions

physics
A curcial part of a piece of machinery starts as a flat uniform cylindrical disk of radius R0 and mass M. It then has a circular hole of radius R1 drilled into it. The hole's center is a distance h from the center of the disk. Find … 
physics
a uniform disk and a uniform sphere are rolled down an incline plane from the same point and intially they are at rest. Find the difference in time they arrive at a mark on the plane which is 6 meters from the starting point. The sphere … 
physics
a uniform disk and a uniform sphere are rolled down an incline plane from the same point and intially they are at rest. Find the difference in time they arrive at a mark on the plane which is 6 meters from the starting point. The sphere … 
PHYSICS
A charged disk of radius R that carries a surface charge density รณ produces an electric field at a point a perpendicular distance z from the center of the disk, given by: Consider a disk of radius 10 cm and positive surface charge … 
Physics
A charged disk of radius R that carries a surface charge density σ produces an electric field at a point a perpendicular distance z from the center of the disk, given by: Edisk = (sigma/2e0) x(1(z/(square root(z^2 + R^2)) Consider … 
Physics
A machine part is made from a uniform solid disk of radius R and mass M. A hole of radius R/2 is drilled into the disk, with the center of the hole at a distance R/2 from the center of the disk (the diameter of the hole spans from … 
Physics
A solid cylindrical disk has a radius of 0.18 m. It is mounted to an axle that is perpendicular to the circular end of the disk at its center. When a 40N force is applied tangentially to the disk, perpendicular to the radius, the … 
Physic
A machine part is made from a uniform solid disk of radius R = 0.161 m and mass M = 7.75 kg. A hole of radius R/2 is drilled into the disk, with the center of the hole at a distance R/2 from the center of the disk (the diameter of … 
Physics Repost
A at disk of material has the same mass as the Earth, 5.98E+24 kg, and has a radius of 6.25 E+07 m. Point A is located a distance of 5.8E+06 m above the center of the disk. Point B is located right at the center of the disk. Treat … 
physics
A disk with mass m = 8.1 kg and radius R = 0.33 m begins at rest and accelerates uniformly for t = 18 s, to a final angular speed of ω = 34 rad/s. What is the angular acceleration of the disk?