Tough GPE Question! (1 Viewer)

[viviansidiss]

An object is stationary in space and located at a distance 10000km from the centre of a certain planet.It is found tha 1.0MJ of work needs to be done to move the object to a stationary point 20000km from centre of planet. Calculate how much more work need to be done to move the object to stationary point 80000km from centre of planet

 

[me121]

An object is stationary in space and located at a distance 10000km from the centre of a certain planet.It is found tha 1.0MJ of work needs to be done to move the object to a stationary point 20000km from centre of planet. Calculate how much more work need to be done to move the object to stationary point 80000km from centre of planet

if this is the same as that hsc question... i wrote up a solution http://hscphysics.googlepages.com/Phys_Past_Paper_Sol.pdf

 

[k02033]

Let a=10000km b=20000km c=80000km

let system be the object and earth, external agent is whatever is moving the objects

work done by external agent = change in potenial energy within system+ change in kinetic energy within the system.



Lets first use this on the 1st trip that required 1.0MJ

so

is zero since object is stationary at end pts.



plug in a and b and we can find a value for GmM. (so the reason that they give us the values in 1st trip was just to let us get a value for GmM)

now for the second trip



we know GmM, c, b, simply plug and pull answer

 

[viviansidiss]

the derivative of cos2x is -2sin2x (in reference to your sig)

Thanks I was thinking of integral

 

[addikaye03]

Thanks I was thinking of integral

sorry to be pety, but even if it was integral it would still be wrong

 

[lyounamu]

sorry to be pety, but even if it was integral it would still be wrong

lol

 

[addikaye03]

lol

i really felt like a shit bloke writing that haha