general science physics problems

ave123

hey, i dunno if this is the right place to post this but im in desperate need:L...im stuck on a physics problem that goes like this: On earth, two parts of a space probe weigh 14200 N and 2990 N. These parts are separated by a center-to-center distance of 19.9 m and may be treated as uniform spherical objects. Find the magnitude of the gravitational force that each part exerts on the other out in space, far from any other objects....i thought i knew how to do it but i think its more complicated then i first thought......anyone else feel free to post here there physics problems:L

wmirl

You're given the weight, use [latex] W = mg [/latex] to work out their masses, then plug into Newton's Law of Gravitation to figure out the force they exert on each other.

ave123

thanks...i did get it sorted in the end...what i did wrong was convert 19.9 metres into kilometers...im still not sure why i had to leave it in metres, but if its right, its right isuppose

wmirl

ave123 wrote: »

thanks...i did get it sorted in the end...what i did wrong was convert 19.9 metres into kilometers...im still not sure why i had to leave it in metres, but if its right, its right isuppose

You need to have the same units when plugging into the Newton's Law formula. If you look at the gravitational constant units, it has metres in it. Mixing the two will result in the scale being out ([latex]10^3[/latex] in your case). This doesn't just apply to this case, it's applicable in all formulae.

Peregrine

Never input anything into a formula unless it's in SI units.

If the question gives you time in minutes, convert to seconds, centimetres to metres, kilo Newtons to Newtons, grams to kilograms and so on.

wmirl

Nimr wrote: »

Never input anything into a formula unless it's in SI units.

If the question gives you time in minutes, convert to seconds, centimetres to metres, kilo Newtons to Newtons, grams to kilograms and so on.

Not always true. Context is king. Little point converting to SI units, say, for the the equations of motion if the answer for time is needed in hours and everything's given in km, hrs etc. All you have to be is consistent.

Half Rhodesian

ave123 wrote: »

hey, i dunno if this is the right place to post this but im in desperate need:L...im stuck on a physics problem that goes like this: On earth, two parts of a space probe weigh 14200 N and 2990 N. These parts are separated by a center-to-center distance of 19.9 m and may be treated as uniform spherical objects. Find the magnitude of the gravitational force that each part exerts on the other out in space, far from any other objects....i thought i knew how to do it but i think its more complicated then i first thought......anyone else feel free to post here there physics problems:L

hey, mark langs class by any chance?
only seeing your post now and prob too late but answer was 3.31e-7 (N), you may still get half marks though