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Homework Statement
A 2800-kg space vehicle, initially at rest, falls vertically from a height of 3300km above the Earth's surface. Determine how much work is done by the force of gravity in bringing the vehicle to the Earth's surface.
**I read my textbook's method and I got confused. Please take a look at my questions at the bottom of this post.
Homework Equations
See part three.
The Attempt at a Solution
Here is my textbook's method.
I am confused:
1) Why do we have to use the negative vector form of the universal law of gravity?
2) The distance changes from 3300 km to 0 km (Earth's surface). All of the numbers between 0 and 3300 are positive, so is that why ##d \vec l ## is positive?
3) Where did ##d \vec l = dr \vec r ## come from?
4) During the integration ##\vec r ## vanishes. Why is that?
Thank you.