kinetic energy and velocity? (1 Viewer)

[kkk579]

for a satellite in orbit, as it gets closer towards earth the kinetic energy increases, but somehow the velocity decreases? is it because to calculate the kinetic energy of a satellite you use vorb which should only be used when a satellite is in a stable orbit, and since this satellite is technically unstable since it is falling back towards earth vorb doesnt apply anymore? but how would this work because that means kinetic energy would be decreasing which opposes whats supposed to happen. i have a test tmrw on this pls reply asap thank you

 

[wollongong warrior]

but somehow the velocity decreases?

what?



Velocity doesn't decrease when r decreases?

 

[liamkk112]

for a satellite in orbit, as it gets closer towards earth the kinetic energy increases, but somehow the velocity decreases? is it because to calculate the kinetic energy of a satellite you use vorb which should only be used when a satellite is in a stable orbit, and since this satellite is technically unstable since it is falling back towards earth vorb doesnt apply anymore? but how would this work because that means kinetic energy would be decreasing which opposes whats supposed to happen. i have a test tmrw on this pls reply asap thank you

suppose you decrease in altitude. then GPE -> KE, so the speed has to increase (if higher kinetic energy and constant mass, the speed of the object has to increase)

i wouldn't get caught up in the formulas too much, just use conservation of energy, and common sense, if you have more kinetic energy you are moving faster

 

[kkk579]

what?



Velocity doesn't decrease when r decreases?

No as in a satellite falling back to earth not like a satellite moving from a stable orbit further from earth to another stable orbit closer to eaeth

 

[kkk579]

No as in a satellite falling back to earth not like a satellite moving from a stable orbit further from earth to another stable orbit closer to eaeth

Like it begins to lose velocity then it js starts ti gradually drift back to earths surface

 

[kkk579]

suppose you decrease in altitude. then GPE -> KE, so the speed has to increase (if higher kinetic energy and constant mass, the speed of the object has to increase)

i wouldn't get caught up in the formulas too much, just use conservation of energy, and common sense, if you have more kinetic energy you are moving faster

But as a satellite begins to lose velocity doesnt it drift back to earth?

 

[kkk579]

For example this q the answer is D

 

[wollongong warrior]

For example this q the answer is DView attachment 46032

I feel like that's just process of elimination. A and B are immediately disregarded because they don't make sense. If the orbital speed is reduced by half then C doesn't really make sense since it shows that the satellite practically falls straight back down. Hence the only option left is D

 

[liamkk112]

But as a satellite begins to lose velocity doesnt it drift back to earth?

in reality yes, lookup orbital decay. but, for simplification (as you do in most physics questions), if you assume that there is 0 energy loss, and the velocity points in the ideal direction such that the gravitational force will make the satellite move in a perfect circle, then there is no drift

For example this q the answer is DView attachment 46032

for this question, the key point is that the probe's velocity is halved. we know that, F = mv^2/r = GMm/r^2 for circular motion to occur. say that this occurs at some velocity v_0, which the probe P was at before it's velocity was halved
hence, if the velocity is halved to v_0/2, then the gravitational force is going to be too strong compared to the altitude of the satellite, so the satellite will be pulled in (and hence drift inwards)