Physics: Principles with Applications (7th Edition)

Published by Pearson
ISBN 10: 0-32162-592-7
ISBN 13: 978-0-32162-592-2

Chapter 4 - Dynamics: Newton's Laws of Motion - General Problems - Page 108: 94

Answer

(a) $a = 3.1 ~m/s^2$ (b) $F_T = 2.0~N$

Work Step by Step

(a) Let's consider the system of both blocks. We can use a force equation to find the acceleration. Let $m_A$ and $m_B$ be $m$ since both blocks have the same mass. $(2m)a = \sum F$ $2ma = 2mg ~sin(\theta) - mg ~cos(\theta)\cdot \mu_A - mg ~cos(\theta)\cdot \mu_B$ $2a = 2g ~sin(\theta) - g ~cos(\theta)\cdot (0.20) - g ~cos(\theta)\cdot (0.30)$ $2a = 2g ~sin(\theta) - g ~cos(\theta)\cdot (0.50)$ $2a = 2g ~sin(\theta) - 2g ~cos(\theta)\cdot (0.25)$ $a = g ~sin(\theta) - g ~cos(\theta)\cdot (0.25)$ $a = (9.80 ~m/s^2) ~sin(32^{\circ}) - (9.80 ~m/s^2) ~cos(32^{\circ}) \cdot (0.25)$ $a = 3.1 ~m/s^2$ (b) Let's consider the system of block B. We can use a force equation to find the tension $F_T$ in the cord: $\sum F = ma$ $F_T + mg ~sin(\theta) - mg ~cos(\theta) \cdot \mu_B = ma$ $F_T = ma - mg ~sin(\theta) + mg ~cos(\theta) \cdot \mu_B$ $F_T = (5.0 ~kg)(3.1 ~m/s^2) - (5.0 ~kg)(9.80 ~m/s^2) ~sin(32^{\circ}) + (5.0 ~kg)(9.80 ~m/s^2)~cos(32^{\circ})\cdot (0.30)$ $F_T = 2.0~N$
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