1. R
    Standard memberRemoved
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    30 Jan '10 02:18
    Originally posted by AThousandYoung
    Not in a gravity field.
    True...My Bad
  2. R
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    30 Jan '10 07:17
    I should have said "Net" acceleration
  3. Standard memberwolfgang59
    Quiz Master
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    30 Jan '10 11:20
    Originally posted by TheMaster37
    Enlighten us wolfgang, where exactly does his line of reasoning go wrong?

    We alraedy know that at least one of them is wrong, seeing as they produce diferent answer.
    The more I look at this the more confusing it becomes.

    The maths is easy but the physical implications seem wrong.

    I've started a new thread which I hope you all contribute to
    Kinetic Energy Changes at fast speeds
  4. Standard memberAThousandYoung
    Shoot the Squatters?
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    09 Feb '10 21:29
    Originally posted by AThousandYoung
    Let me try this again.

    There is a little robotic space probe floating out in space that is not accelerating. We can take it's inertial frame of reference as v=0.

    The engine, when on, provides 1 watt of power which is converted to kinetic energy. The probe has a mass of 2 kg. After one second, the probe has 1 J of kinetic energy, and it's veloc ...[text shortened]... to the probe's original velocity
    four seconds ago.

    Why am I getting different answers?[/b]
    An extremely intelligent person whom I shall call BrotherGeeWhiz commented on my confusion:

    Power and Velocity. I think the issue would be resolved if you took into account the acceleration, which is the quantity I like to think about in classical mechanics. It's proportional to force and invariant to changes in inertial reference frames. If one proposes some continuous form for the acceleration, then the velocities should add along different reference frames (as long as v<<c).

    Also (tiny point), for an isolated mass in space to move, it has to propel some "fuel" in the opposite direction to conserve momentum. This changes the mass, but since the fuel can move arbitrarily fast, the change in mass can be made arbitrarily small.
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