Potential Energy of Point-Charges: an Alpha Particle Is a Nucleus

question 54

Multiple Choice

Potential energy of point-charges: An alpha particle is a nucleus of helium. It has twice the charge and four times the mass of the proton. When they were very far away from each other, but headed toward directly each other, a proton and an alpha particle each had an initial speed of 0.0030c, where c is the speed of light. What is their distance of closest approach?

Hint: There are two conserved quantities. Make use of both of them. (c = 3.00 × 10⁸ m/s, k = 1/4πε0 = 8.99 × 10⁹ N ∙ m²/C², e = 1.60 × 10^-19 C, mproton = 1.67 × 10^-27 kg)

• A) 2.1 × 10^-13 m
• B) 3.3 × 10^-13 m
• C) 2.6 × 10^-13 m
• D) 2.9 × 10^-13 m

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Definitions:

Intercourse

The act of sexual contact between individuals, often referring specifically to penile-vaginal penetration.

Conceptus

The embryo and its associated membranes and structures from conception until development into a recognizable fetus.

Amniotic Sac

A sac that holds the embryo (and later fetus). Also called the bag of water.

Chorion

The embryo’s outermost membrane.