Why sometimes momentum seemed to be not conserved???

From the textbook,

it only mentioned that may be the total mass of the object is too large...

But is it the only reason?

I faced a question from the pastpaper in HKCEE 1998 Q2dii

When a metal ball fired by a cannon hit an object.

Both of them is at rest at last.

Is it because the total mass of the object(unknown mass) and the metal ball(10kg moves with constant seped 100m/s) is too large

so that motion cannot be detected and momentum seemed not conserved???

2 Answers

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  • 1 decade ago
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    momentum has nothing to do with the size of an object. Your textbook seems wrong ar...

    Momentum cannot be conserved due to external forces acting against it. Such as your metal ball encounters air resistance and loses energy to it's surroundings as heat. THe cannon is stopped because of friction from it's moving part and wheels to the ground friction. Momentum can't be conserved due to loss of energy (friction, air resistance, heat) to the surroundings.

    Popular example is "Newton Balls" Seem to go on forever, but heat loss and moving parts are not perfectly made (minor imperfections) so they will stop eventually. Or even pendulum...air resistance, etc......

  • 1 decade ago

    momentum要consver要no external force

    所以你見親o既題目用momentum黎計的都會係打橫

    而不是打直因為打直有個gravitational force act左落d object

    Source(s): myself=]
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