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Why is the following situation impossible? An air rifle is used to shoot 1.00-g particles at a speed of vx = 100 m/s. The rifle’s barrel has a diameter of 2.00 mm. The rifle is mounted on a perfectly rigid support so that it is fired in exactly the same way each time. Because of the uncertainty principle, however, after many firings, the diameter of the spray of pellets on a paper target is 1.00 cm.
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The mass of the particles is , and their speed is . The diameter of the hole is . We need to find the distance (see the attached picture). From , we can write:
and we choose the case when has the smallest value , where is the reduced Planck's constant . Also, from the similarity of the blue and the green triangles at the picture, we can write:
where is the momentum of the particles along axis. Now, we will express as:
and substitute at the Heisenberg principle:
Rearrange:
Substitute numerical values:
Clearly, the required distance is larger than the diameter of the visible Universe .
The distance x is 190 times larger than the observable Universe!
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