University Physics with Modern Physics (14th Edition)

Published by Pearson
ISBN 10: 0321973615
ISBN 13: 978-0-32197-361-0

Chapter 8 - Momentum, Impulse, and Collision - Problems - Exercises - Page 267: 8.66

Answer

One puck makes an angle of $60^{\circ}$ north of east, and the other puck makes an angle of $60^{\circ}$ south of east.

Work Step by Step

By conservation of momentum, $p_x= 0$ and $p_y = 0$. Let's assume that puck A moves west. Let $v$ be the speed of each puck. $p_x = 0$ $0 = -m_Av+mv_{Bx}+mv_{Cx}$ $v = v_{Bx}+v_{Cx}$ $p_y = 0$ $0 = 0 +mv_{By}+mv_{Cy}$ $v_{By} = -v_{Cy}$ The vertical components of puck B and puck C have the same magnitude. Therefore, the horizontal components of puck B and puck C must have the same magnitude, otherwise they would have different speeds. Then $v_{Bx} = \frac{v}{2}$ and $v_{Cx} = \frac{v}{2}$. Since $\cos(60^{\circ}) = 0.5$, puck B and puck C must make an angle of $60^{\circ}$ with the +x-axis. Because their vertical components are in the opposite directions, one puck makes an angle of $60^{\circ}$ north of east, and the other puck makes an angle of $60^{\circ}$ south of east.
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