Question

help @Mathematics

Answer 1

anyon?

Answer 2

hi

Answer 3

what do you need?

Answer 4

:) work is a scalar quantity .same for energy then y do they hav negative and + signs?

Answer 5

because real numbers can be positive or negative.

Answer 6

??

Answer 7

y a satellite hav negative potential energy??

Answer 8

For example, when I pick up a book from the floor, I am doing work (against gravity), that is positive work. If I pick up a book from the table and put in on the floor I am doing negative work.

Change in the energy is the really the key thing.

Now, with your satellite example ...

Answer 9

because we want a way to quantitatively measure change in gravitational potential energy, i.e., write down a formula for it, we have to assign some place zero gravitational potential energy.

Answer 10

then y work done to put a satellite into a planets gravitational field is negative?

Answer 11

It could be anywhere. It could be the center of the earth, it could be at the point half way between the earth and the moon, it could be at my house. But analytically we choose it at infinity.

This absolute and arbitrary assignment of zero gravitational potential is arbitrary and its absolute level isn't important. But that choice of zero make it easier, because if we choose infinity and bring an object to a distance R from the earth, we can then show it has gravitational potential energy of
\[ - \frac{GM}{r} \]
where M is the mass of the earth and G is the gravitational constant.

Answer 12

So with the satellite, yes, it does have negative potential energy only because we chose zero to be at infinity.

Answer 13

However, the there is still positive work to be done to get the satellite from the surface of the earth into orbit: we go from a larger negative value of PE to a smaller negative value.

Answer 14

what is r here>

Answer 15

the radial distance from the earth.

Answer 16

how ??

Answer 17

u see the bodys displacemrnt is from some point at infinity to inside gravitational field

Answer 18

r should be that ryt?

Answer 19

also y change in P E is work done here??i thought change in K E is work done

Answer 20

Watch this lecture. He explains it all here clearly with diagrams, which I'd do with you if we were in the same room:
http://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/lecture-11/

Answer 21

Work done is the change in any and all energies, whether it be PE, KE, chemical energy, radiant energy, nuclear energy, ....

Answer 22

y it is PE here ?? i thought there is change i n KE??

Answer 23

What question exactly are we discussing now?

Answer 24

lotz of doubtyz lol

Answer 25

Watch the lecture:
http://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/lecture-11/

Answer 26

This is an awesome lecture. Make sure you watch it right to the end.

Answer 27

WOW! It's long!