A child\'s toy consists of two flat magnetic disks with holes in them, which can

Question

A child's toy consists of two flat magnetic disks with holes in them, which can be threaded onto a vertical dowel. If the magnets are arranged properly (so that they repel), the top magnet will "float" above the bottom magnet, without making contact with it (see the diagram to the right). If we place the apparatus on a scale with the top magnet floating, how does the scale's measurement compare with the sum of the individual weights of the three objects (the dowel and the two magnets)? a.The scale measures a value equal to the sum of the three weights.b.The scale measures a value greater than the sum of the three weights. c.The scale measures a value less than the sum of the three weights. d.How the scale measurement compares with the sum of the three weights depends upon the amount of friction force between the dowel and the floating weight. e.How the scale measurement compares with the sum of the three weights depends upon which of the two magnets is heavier.

Explanation / Answer

The scale will measure a value equal to thr sum of the three weights.

Since the upper weight is floating, the magnetic force exchanged between the magnets is equal to the eight of the upper magnet.

So, the upper magnet will also appy the same force equal to its weight on the lower magnet.

So, the net force on the scale is equal to the contact weights of the dowel and the lower magnet and the magnetic force applied by the upper magnet, i.e. weight of the upper magnet.

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