# Using uncertainty principle to find momentum of a bullet fired from a rifle and for the velocity of an electron

A 10 g bullet leaves a rifle muzzle at a speed of 120 m/s.

a.) If the uncertainty of the bullet's position is known to the accuracy of the barrel's radius (0.5 cm), what is the minimum uncertainty in the bullet's momentum?

b.) Repeat for an electron. Where the accuracy of its position is known to be +/- 1 angstrom (10-10 m) and its velocity is the same as the bullet's (120 m/s). Mass of the electron is 9.11 x 10-31 kg.

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#### Solution Preview

I will use dp to represent uncertainty in momentum and dx uncertainty in positiion.

a) (dp)(dx) >= 0.5 * hbar

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#### Solution Summary

With full calculations, the problems are solved.

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