20. An electron has been accelerated by a potential difference of 100 V. If its position is known to have an uncertainty of 1 nm, what is the percent uncertainty (Δp/p × 100 %) of the electron? (A) 1% (B) 10% (C) ＞＞10% (D) 20 % (E) ＜＜1%

8. The mass density of a certain planet has spherical symmetry but varies in such a way that the mass inside every spherical surface with center at the center of the planet is proportional to the radius of the surface. If r is the distance from the center of the planet to a point mass inside the planet, the gravitational force on the mass is: (A) not dependent on r (B) proportional to r (C) proportional to r² (D) proportional to 1/r (E) proportional to 1/r²

20. An electron has been accelerated by a potential difference of 100 V. If its position is known to have an uncertainty of 1 nm, what is the percent uncertainty (Δp/p × 100 %) of the electron?
(A) 1%
(B) 10%
(C) ＞＞10%
(D) 20 %
(E) ＜＜1%

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