Question

In the early part of the 20th century, Sir Joseph J. Thomson (discoverer of the electron) proposed a "plum pudding" model of the atom. He believed that the positive charge of the atom was spread out like a pudding and that the negative charges (electrons) were embedded in the pudding like plums. His student Ernest Rutherford performed an experiment in 1911 that disproved the plum pudding model. Rutherford fired a beam of alpha particles (helium nuclei) at a thin metal sheet. Because alpha particles are positive, the plum pudding model predicted that they should only be slightly deflected by the positive pudding. Instead, Rutherford found that the alpha particles were greatly deflected, and some even reversed direction completely. Rutherford was surprised by his results and said that it was like firing a bullet at a tissue paper and seeing it bounce back. Rutherford concluded that the positive charge of the atom was not spread out like pudding, but rather was concentrated in the center or nucleus of the atom. The alpha particles used in the experiment had an initial speed of 2 ✕ 10⁷ m/s and a mass of 6.7 ✕ 10⁻²⁷ kg.

(a) Assuming the nucleus is initially at rest, the collision is head-on and elastic, and the nucleus is much more massive than the alpha particle, find the final speed of the alpha particle after it collides with the nucleus.
_____m/s

(b) Rutherford used gold in his experiment. Check the assumption that the nucleus is much more massive than the alpha particle by finding the speed of the nucleus after the collision.
_________m/s

Answer 1