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Name: Unknown
Status: other
Age: 50s
Location: N/A
Country: N/A
Date: 2000-2001


Question:
How does it explain that we have to do only 190,000 miles on way to moon at speeds like 225,000 miles an hour or so and beyond that moon's graVITY PULLS IN.pLEASE EXPLAIN BASED ON NEWTON'S LAW OF GRAVITY.

The book by ABC science editor says,we have only to worry about first 190,000 miles,rest 50,000 miles are easy to cover since Moon's gravity pulls in the mooncraft. I am asking How Newton's laws come in this;how the relation m1xm2/r2 plays in this.


Replies:
Real simple. The magnitude of the force acting on the spacecraft from the earth's gravity will be GmSmE/(rSE)^2, and the force from the moon's gravity will be GmSmM/(rSM)^2. Here, G is the gravitational constant, mS is the mass of the spacecraft, mE is the mass of the earth, mM is the mass of the moon, rSE is the distance from the spacecraft to the earth, and rSM is the distance from the spacecraft to the moon. These forces will be in the direction toward the earth and toward the moon, respectively. The total force on the spacecraft is the sum of the forces from the earth and the moon (ignoring forces from objects like the sun, Mars, etc...). If the spacecraft is on a line between the earth and the moon, these two forces will act in opposition to each other. When the magnitude of the force from the moon is greater than the magnitude of the force from the earth, then the moon will pull the craft in. By substituting into the formulas the proper values for mE, mM, and the distance from the earth to the moon, you should be able to calculate this distance.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois



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