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Homework Help: Free falling apple

  1. Oct 3, 2006 #1
    when the cable of the life snaps,everything inside experience freefall as the man is not touching the bottom of the lift right?so suppose a man in the lift holds an apple and the cable snaps so the man and apple will experience freefall right? so heres the qn when they are falling and the man were to push the apple upward, will the apple go all the way to the top of the lift or just move a little?

    alrite just thought of this qn so might as well ask it...if you are taking the frame of the man inside the lift,wouldnt the apple be defying N2L?pardon me if i ask this the wrong way coz i have yet to explore this frame of reference of thing :tongue:

    THANKS :wink:
  2. jcsd
  3. Oct 3, 2006 #2
    Yes and yes. That depends on how strong the man pushes the apple. I dont understand how u mean when N2L is violated :uhh: but u should look at it from N3L. The man exerts a force on the apple and the apple will exert an equal and opposite force on the man. Basically if the man pushes the apple 10 N, the man will be pushed back by 10 N and you can calculate the acceleration of the man and the apple using F=ma: where the man accelerates upwards and the apple downwards.
  4. Oct 3, 2006 #3
    oh well u see.....when u are looking from the man inside the lift point of view, there is a gravity acting down on the apple but instead of falling down it is floating?so u consider this the inertial frame?sry if this sound stupid coz i only touch only frame of reference recently
  5. Oct 3, 2006 #4


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    It's not an inertial frame because it's accelerating. However, I can't really think of anything you could do to prove you were in free fall so the laws of physics may still apply as if it were an inertial frame.

    And yes, the apple will seem to float to the ceiling. Ever heard of the vomit comet? It's a plane that flies in a parabolic arc, mimicking the weightlessness astronauts feel when in orbit.
  6. Oct 3, 2006 #5


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    I have a question about this. Isn't 'inertai frame' where you pretend you're sitting still even if you are accelerating and pretend everything else is moving with respect to you?
  7. Oct 3, 2006 #6


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    An inertial reference frame is a frame where Newton's laws of motion are valid. It is either fixed, or moves with constant velocity.
  8. Oct 3, 2006 #7
    Hmm, I'll just bring in the equivalence principle here. Since the man, apple and the lift are accelerating, as far as the occupants of the lift are concerned, gravity does not exist.
    The force of gravity is of course always acting and will continue to act on them, however since the whole system is accelerating, the apple and the man would not feel gravity here. Ie: until the lift actually hits something - there is no gravity!
    All of Newton's Laws are still obeyed - except for the fact that the force of gravity does not exist as far as the system is concerned.
  9. Oct 3, 2006 #8


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    ah, I see. It requirs a constant velocity
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