Dekoyl's Questions

[dekoyl]

^Yeah I thought so too. I used like but they used :S

[TrueTears]

Yea I used 700N as well dekoyl, like Mao said, it's just the area under the graph...

[dekoyl]

Alright =] Thanks for the confirmations

[dekoyl]

I've got a few discrepancies between a few sets of notes.

For questions regarding orbits/satellites, do we always use the given radius of the satellite's orbit?

In one of the questions uploaded here, there is:
Radius of satellite:
and Radius of satellite's orbit:

Which one do we use and in what cases?

Thanks! (I have a SAC tomorrow)

[TrueTears]

Yes here's the trick examiners might use, if they say "orbit" that's the distance you use for "r"

But if they say "altitude" or "height" you must add the earth's radius, or whatever planet the satellite is orbiting.

[dekoyl]

Thanks TT!

So in the example I gave above, the "Radius of satellite" is pretty much a useless figure?

[TrueTears]

Yeah, I would use the "Radius of satellite's orbit" as the value for "r"

[dekoyl]

The magnitude of the gravitational field strength on the surface of the Earth has a value of approximately 10 N/kg.
Calculate the magnitude of the gravitational field strength at a distance of four Earth radii above the surface.

I  used which got the right answer but they wanted something with:
. Where did this formula come from?

Thanks

[dcc]

Basically, they are acknowledging that , from which the answer easily falls out (without needing to do any calculations).

[kurrymuncher]

The magnitude of the gravitational field strength on the surface of the Earth has a value of approximately 10 N/kg.
Calculate the magnitude of the gravitational field strength at a distance of four Earth radii above the surface.

I  used which got the right answer but they wanted something with:
. Where did this formula come from?

Thanks

They got that formula just by using this .Just divide g1 by g2. As G and M are the same in each case they will just cancel out so you will be left with

[methodsboy]

^i believe that's one of kepler's laws

[kamil9876]

from my raw memory, i don't think it is. Johann Kepler was an astronomer and he lived before Newton, hence his work wouldn't have anticipated anything about acceleratation due to gravity being related to celestial motion. His work was more to do with planetary motion like radius of orbits and periods (i think he was the first to prove that the orbits are elliptical). Though he never anticipated anything about forces or acceleration, I think he believed that magnetism or some whirlpool moved the planets at some point. 

[dekoyl]

Q:A vehicle with constant acceleration travels 20m in 2s and 13m in the next second. What is the acceleration?

Thanks =\

[Damo17]

Q:A vehicle with constant acceleration travels 20m in 2s and 13m in the next second. What is the acceleration?

Thanks =\

let u= initial velocity, a =acceleration

since 3 seconds total:

    -----1


                   -----2

       -----1
    -----2

solve simultaneous equations for u gives

    ,

[kamil9876]

Assuming the direction doesn't change:

x=0.5at^2+ut

x=20, when t=2:
20=2a+2u

x=20+13 when t=3:
20+13=4.5a+3u

Simultaenous equations ftw.
=============================================================
Interestingly, say the direction of motion changed at t=2:

we still have the equation:

20=2a+2u

Only this time:

20-13=4.5a+3u


Gotta love unprecise questions.