Authors: Russell C. Hibbeler
ISBN-13: 978-0133915426
See our solution for Question 8P from Chapter 20 from Hibbeler's Engineering Mechanics.
We are given the angular velocity of shaft in z-axis is ${\omega _z} = 4\;{\rm{rad/s}}$, and the angular acceleration of the shaft along z-axis is ${\left( {{{\dot \omega }_1}} \right)_{xyz}} = 2\;{\rm{rad/}}{{\rm{s}}^2}$.
We are asked to determine the velocity and the acceleration of point A on the disk at the instant.
The diagram of the system is shown as:

We have the radius of the disk is $r = 0.1\;{\rm{m}}$.
We have the distance between disk and shaft end is $l = 0.5\;{\rm{m}}$.
We have the position vector of point A on the disk is ${r_A} = \left( {0.5i + 0.1k} \right)\;{\rm{m}}$.
The expression to calculate the total angular velocity of the disk is,
\[\omega = {\omega _1} + {\omega _2}\]Substitute the values in the above expression.
\[\omega = \frac{5}{{\sqrt {26} }}\omega i - \frac{1}{{\sqrt {26} }}\omega k\] … (1)Now, substitute the value of $\omega $ component on the left side, we get,
\[( - 4k + {\omega _2}i) = \frac{5}{{\sqrt {26} }}\omega i - \frac{1}{{\sqrt {26} }}\omega k\]On comparing $k$ coefficients in the above expression.
\[\begin{array}{c} - 4 = - \frac{1}{{\sqrt {26} }}\omega \\ \omega = 4\sqrt {26} \;{\rm{rad/s}} \end{array}\]On comparing $i$ coefficients in the above expression.
\[\begin{array}{c} {\omega _2} = \frac{5}{{\sqrt {26} }}\omega \\ {\omega _2} = \frac{5}{{\sqrt {26} }}\left( {4\sqrt {26} } \right)\\ {\omega _2} = 20\;{\rm{rad/s}} \end{array}\]Substitute the value of $\omega $ on the right side in the equation (1).
\[\begin{array}{c} \omega = \frac{5}{{\sqrt {26} }}\left( {4\sqrt {26} } \right)i - \frac{1}{{\sqrt {26} }}\left( {4\sqrt {26} } \right)k\\ \omega = \left( {20i - 4k} \right)\;{\rm{rad/s}} \end{array}\]The formula to calculate the rotating angular acceleration with reference to xyz rotating frame is,
\[\frac{{{{\left( {{{\dot \omega }_2}} \right)}_{xyz}}}}{{{{\left( {{{\dot \omega }_2}} \right)}_{xyz}}}} = \frac{l}{r}\]Substitute the values in the above expression.
\[\begin{array}{c} \frac{{{{\left( {{{\dot \omega }_2}} \right)}_{xyz}}}}{{{{\left( {{{\dot \omega }_2}} \right)}_{xyz}}}} = \frac{{0.5}}{{0.1}}\\ {\left( {{{\dot \omega }_2}} \right)_{xyz}} = 5{\left( {{{\dot \omega }_1}} \right)_{xyz}} \end{array}\]The formula to calculate the rotating angular velocity with reference to xyz rotating frame is,
\[\Omega = {\omega _1}\]Substitute the values in the above expression.
\[\Omega = - 4k\;{\rm{rad/s}}\]The formula to calculate the rotating angular acceleration of the frame is,
\[{\dot \omega _2} = {\left( {{{\dot \omega }_2}} \right)_{xyz}} + \Omega \times {\omega _2}\]Substitute the values in the above expression.
\[\begin{array}{c} {{\dot \omega }_2} = 10i + \left( { - 4k} \right) \times \left( {20i} \right)\\ {{\dot \omega }_2} = \left( {10i - 80j} \right)\;{\rm{rad/}}{{\rm{s}}^2} \end{array}\]The formula to calculate the rotating angular acceleration of the frame is,
\[{\dot \omega _1} = {\left( {{{\dot \omega }_1}} \right)_{xyz}} + {\omega _1} \times {\omega _1}\]Substitute the values in the above expression.
\[\begin{array}{l} {{\dot \omega }_1} = - 2k + \left( {\frac{5}{{\sqrt {26} }}\omega i \times \frac{5}{{\sqrt {26} }}\omega i} \right)\\ {{\dot \omega }_1} = \left( { - 2k} \right)\;{\rm{rad/}}{{\rm{s}}^2} \end{array}\]The formula to calculate the final rotating angular acceleration of the shaft is,
\[\alpha = {\dot \omega _1} + {\dot \omega _2}\]Substitute the values in the above expression.
\[\begin{array}{c} \alpha = \left( { - 2k} \right)\;{\rm{rad/}}{{\rm{s}}^2} + \left( {10i - 80j} \right)\;{\rm{rad/}}{{\rm{s}}^2}\\ \alpha = \left( {10i - 80j - 2k} \right)\;{\rm{rad/}}{{\rm{s}}^2} \end{array}\]The formula to calculate the velocity of point A on the disk is,
\[v = \omega \times {r_A}\]Substitute the values in the above expression.
\[\begin{array}{c} v = \left( {20i - 4k} \right)\;{\rm{rad/s}} \times \left( {0.5i + 0.1k} \right)\;{\rm{m}}\\ v = \left( { - 4j} \right)\;{\rm{m/s}} \end{array}\]The formula to calculate the acceleration of point A on the disk is,
\[{a_A} = \left( {\alpha \times {r_A}} \right) + \left( {\omega \times v} \right)\]Substitute the values in the above expression.
\[\begin{array}{c} {a_A} = \left[ {\left( {10i - 80j - 2k} \right) \times \left( {0.5i + 0.1k} \right)} \right] + \left[ {\left( {20i - 4k} \right) \times \left( { - 4j} \right)} \right]\\ {a_A} = \left( { - 24i - 2j - 40k} \right)\;{\rm{m/}}{{\rm{s}}^2} \end{array}\]