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  1. FruitNinja

    Planet orbiting around a star whose mass changes

    yes, I know it is really not circular but It will be assumed in this probem. I used f=ma to come up with vi=sqrt(GM/ri) & vf=sqrt(GM/2rf)and plugged in those as V on both sides (with the corresponding r) I got 2 ri = rf
  2. FruitNinja

    Planet orbiting around a star whose mass changes

    1. Homework Statement (Assuming all circular orbits) Say there is a star with mass M and a planet orbiting that star with a mass m. The star M then suddenly loses half of its mass. (So now it is M/2) What is the new radius of orbit of the planet around the star? Warning: Velocity will not be...
  3. FruitNinja

    ORBIT: change in orbital distance

    Thank you for the help gneill! I'll try that when I get the chance.
  4. FruitNinja

    ORBIT: change in orbital distance

    Yes, doing f=ma I got v^2 =GM/r. Now I have v in terms of r, G, & m. This must be it. So now I would be able to use conservation of angular momentum
  5. FruitNinja

    ORBIT: change in orbital distance

    Ok, I came up with this: but I don't know the initial/final velocities of the moon. I could use 2 pi r / T if I was given T but I am not r x p = rp (since right angle) Iω + r x p = Iω + r x p IEarth ωearth initial + dinitial vinitial mmoon = IEarth ωearth final + dinitial vfinal mmoon
  6. FruitNinja

    ORBIT: change in orbital distance

    Because the earth would not be a perfect sphere anymore right? So would I use momentum conservation in this one with the moon being r x p?
  7. FruitNinja

    ORBIT: change in orbital distance

    Oh I understand how the earth slows down now. But why does this affect the moon's orbit? Because the force of gravity doesn't change because the earth does not become more massive or something
  8. FruitNinja

    ORBIT: change in orbital distance

    1. Homework Statement we know the mass of the moon, Mm, and the earths, Me, and also the initial distance between their centers as the moon orbits the earth, Rem. Now if the earth’s angular velocity about its own axis is slowing down from a initial given angular velocity, ωi to a final angular...
  9. FruitNinja

    Potential Energy function for this system

    So is it asking for the change of PE from the y position to the equilibrium? Because there needs to be some kind of change
  10. FruitNinja

    Potential Energy function for this system

    But I don not understand how that would help with finding the change in potential energy of the system since this isn't an f=ma problem
  11. FruitNinja

    Potential Energy function for this system

    I mean the tension force is upward (direction) Edit: I mean for the outer blocks it is upward. for the middle one it is at an angle
  12. FruitNinja

    Potential Energy function for this system

    Supported? By the 2 tension forces of the 2 outer blocks upward. But that would be internal
  13. FruitNinja

    Potential Energy function for this system

    Hmm so I guess if we think of them as 3 separate PEs then 2 of them are decreasing when the 3rd is increasing. so that would change pe. i see that now. But still, the whole system looks static, like it is not moving or changing. Is there some kind of force that would push the middle one down...
  14. FruitNinja

    Potential Energy function for this system

    1. Homework Statement Find the potential energy function for the three mass, earth, and pulley system as shown. The potential energy will be as a function of the vertical position downward as shown in the diagram. Also, find the equilibrium position of this system. The two outside masses are...
  15. FruitNinja

    Time it takes for block to slide down an incline in elevator

    Yes, if we were not in a elevator yes. But that would be a non-inertial frame so we can't do that, according to my teacher
  16. FruitNinja

    Time it takes for block to slide down an incline in elevator

    Ok, It's just Fg and Fn. Those are the only 2 forces acting on the block. for X: -mgsinΘ , no fn here and for Y: -mgcosΘ+Fn
  17. FruitNinja

    Time it takes for block to slide down an incline in elevator

    yeah I did that in the equation above. for the y, -mgcosΘ+Fn are the 2 forces acting on the block. (slanted frame). amgy just means the acceleration of the mass relative to the ground in the y direction
  18. FruitNinja

    Time it takes for block to slide down an incline in elevator

    -mgsinΘ = mamgx for the x and -mgcosΘ+Fn=mamgy for the y are the x and y components of f=ma for the block, but I am using a slanted coordinate frame
  19. FruitNinja

    Time it takes for block to slide down an incline in elevator

    Yes, Amg is acceleration of m relative to g Aeg is acceleration of elevator relative to ground. Since I cannot use fictitious forces I need to use relative accelerations. Amg=Ame+Aeg just shows that the a of the mass relative to the ground is the sum of the 2 relative accelerations vectors
  20. FruitNinja

    Time it takes for block to slide down an incline in elevator

    1. Homework Statement MECHANICS: Given Theta, L, M, and acceleration of elevator relative to ground. Find the time it takes for the block to reach the end of the incline. Here is a diagram: http://k-elahian.com/tmp/nip.PNG [Broken] 2. Homework Equations f=ma kinematics relative...
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