centripetal force question (1 Viewer)

[ratcher0071]

F=mv² / r

does the "r" mean, for example a satellite above the Earth, "the radius of Earth + altitude at which the satellite is at" ?

 

[clintmyster]

r is radius, so if your given any kind of radius thats what your replace in your eqn

 

[ratcher0071]

r is radius, so if your given any kind of radius thats what your replace in your eqn

Ok, for example:

1) You're given the radius 8 000 km, you put 8 000 000 m into "r"

2) You're given the altitude 2 000 m, you put "radius of Earth (6.38 x 10⁶ m) +
2 000 m" = 6.382 x 10⁶ m into "r"

right ??

 

[clintmyster]

well for 1) yes im sure.
for 2) ums thats seems right, thought it would help If I knew the question.

 

[ratcher0071]

A satellite of mass 70kg is travelling at 100m/s at an altitude of 4 000 m above the Earth's surface. Calculate the Centripetal Force acting on the satellite.

 

[clintmyster]

yeah so for that you would add like you did. I'm guessing you can do the calculation. Are you getting a headstart into the space topic? Just wondering tho, did you not learn this in prelim?

 

[MasterYoda]

in the centripetal force equation the "r" is the distance between the CENTRES of 2 masses.

Eg. if you are asked to calculate the centrepetal force acting on the moon due to the earth - you take "r" as the distance from the centre of the earth to the centre of the moon.
if its the force between a satellite and the earth -
- then "r" is the altitude of the satellite and the radius of the earth

both 1) and 2) are correct

 

[ratcher0071]

yeah so for that you would add like you did. I'm guessing you can do the calculation. Are you getting a headstart into the space topic? Just wondering tho, did you not learn this in prelim?

Yeah I can do the calculation:
F= mv²/r
F= 70 x 100² / (6.38 x 10⁶ + 4 000)
F= 700000/6.384 x 10⁶
F= 0.11 N

I am getting a head start in the Space Topic. My stupid Yr 11 textbook (Physics Contexts 1) doesn't have shit about centripetal force. I had to go onto the internet.

 

[ratcher0071]

Eg. if you are asked to calculate the centrepetal force acting on the moon due to the earth - you take "r" as the distance from the centre of the earth to the centre of the moon.

Would the mass be:

a) total mass (earth + moon)
b) mass of earth
c) mass of moon

since;
F_centripetal = mv² /r

 

[miche11e]

wow. your keen. The only thing i got a head start in was 3unit and that was because we'd finished prelim ages before lol.

to the above question, its the mass of the object so the mass of the moon

 

[ratcher0071]

wow. your keen. The only thing i got a head start in was 3unit and that was because we'd finished prelim ages before lol.

to the above question, its the mass of the object so the mass of the moon

Well i should get started in 3unit, but i can't bothered. Because I like Physics more than 3unit maths.

thanks for answering my question

 

[MasterYoda]

Would the mass be:

a) total mass (earth + moon)
b) mass of earth
c) mass of moon

since;
F_centripetal = mv² /r

"m" is the mass in kg of the body that is rotating
"v" is the linear (tangential) velocity in m/s

 

[cutemouse]

Isn't centripetal acceleration basically Preliminary stuff?

 

[Continuum]

Isn't centripetal acceleration basically Preliminary stuff?

Depends on how far you got into the Moving About topic.

 

[Aerath]

Isn't centripetal acceleration basically Preliminary stuff?

Yeah, should be.
We learnt it like 4th week of first term. But then again, some people do Moving About third, but they still should've completed it.

 

[dolbinau]

In the case of orbiting satellites, Universal gravitation formula can be used to find Centripetal force right? (Equal to centripetal force equation, but with different variables of course).

 

[Continuum]

Yeah since it is the centripetal force.

You can also equate one another to give the equation for the escape velocity needed for any object on a planet.

 

[dolbinau]

You mean orbital velocity. I think Escape velocity you make gravitational equal to kinetic energy.

 

[Continuum]

Oops, yep yep, I made a mistake. It's orbital velocity.

 

[dolbinau]

Are you accelerating or have you just learnt this, or do you learn this all yourself? It's so strange there is so many '09ers who appear to know more than us >