Question Number 161783 by ajfour last updated on 22/Dec/21
Commented by ajfour last updated on 22/Dec/21
$${Cylinder}\:{is}\:{free}\:{to}\:{purely}\:{roll},\:{find} \\ $$$${radius},\:{if}\:{point}\:{mass}\:{ball}\:{is}\:{to}\:{be} \\ $$$${received}\:{successfully}. \\ $$
Commented by ajfour last updated on 22/Dec/21
Left d job, shall hunt online..
Commented by mr W last updated on 22/Dec/21
$${welcome}\:{back}\:{sir}! \\ $$
Commented by ajfour last updated on 22/Dec/21
$${thank}\:{you}\:{sir},\:{wont}\:{u}\:{try}\:{this}\:{question}.. \\ $$
Commented by mr W last updated on 23/Dec/21
$${i}'{ll}\:{try}\:{how}\:{far}\:{i}\:{can}\:{go}. \\ $$
Answered by mr W last updated on 23/Dec/21
Commented by mr W last updated on 23/Dec/21
$${x}_{\mathrm{1}} ={s} \\ $$$$\varphi=\frac{{s}}{{R}} \\ $$$${let}\:\omega=\frac{{d}\theta}{{dt}} \\ $$$${x}_{\mathrm{2}} ={s}−{R}\:\mathrm{sin}\:\theta \\ $$$${y}_{\mathrm{2}} ={R}\left(\mathrm{1}+\mathrm{cos}\:\theta\right) \\ $$$${V}=\frac{{ds}}{{dt}}=\omega\frac{{ds}}{{d}\theta} \\ $$$${A}=\frac{{dV}}{{dt}}=\omega\frac{{dV}}{{d}\theta} \\ $$$${N}\:\mathrm{sin}\:\theta\:{R}=\left(\frac{{MR}^{\mathrm{2}} }{\mathrm{2}}+{MR}^{\mathrm{2}} \right)\left(\frac{{A}}{{R}}\right) \\ $$$$\Rightarrow{N}=\frac{\mathrm{3}{MA}}{\mathrm{2}\:\mathrm{sin}\:\theta}=\frac{\mathrm{3}{M}}{\mathrm{2}\:\mathrm{sin}\:\theta}×\frac{\omega{dV}}{{d}\theta} \\ $$$${N}=\mathrm{0}\:\Leftrightarrow\:\frac{{dV}}{{d}\theta}=\mathrm{0} \\ $$$${v}_{{x}} =\frac{{dx}_{\mathrm{2}} }{{dt}}={V}−{R}\:\mathrm{cos}\:\theta\:\omega \\ $$$${v}_{{y}} =\frac{{dy}_{\mathrm{2}} }{{dt}}=−{R}\:\mathrm{sin}\:\theta\:\omega \\ $$$$\frac{{m}}{\mathrm{2}}\left({v}_{{x}} ^{\mathrm{2}} +{v}_{{y}} ^{\mathrm{2}} \right)+\frac{\mathrm{1}}{\mathrm{2}}×\frac{\mathrm{3}{MR}^{\mathrm{2}} }{\mathrm{2}}×\left(\frac{{V}}{{R}}\right)^{\mathrm{2}} ={mgR}\left(\mathrm{1}−\mathrm{cos}\:\theta\right) \\ $$$${v}_{{x}} ^{\mathrm{2}} +{v}_{{y}} ^{\mathrm{2}} +\frac{\mathrm{3}{MV}^{\mathrm{2}} }{\mathrm{2}{m}}=\mathrm{2}{gR}\left(\mathrm{1}−\mathrm{cos}\:\theta\right) \\ $$$${V}^{\mathrm{2}} +{R}^{\mathrm{2}} \omega^{\mathrm{2}} −\mathrm{2}{VR}\omega\:\mathrm{cos}\:\theta+\frac{\mathrm{3}{MV}^{\mathrm{2}} }{\mathrm{2}{m}}=\mathrm{2}{gR}\left(\mathrm{1}−\mathrm{cos}\:\theta\right) \\ $$$$\omega^{\mathrm{2}} −\frac{\mathrm{2}{g}\left(\mathrm{1}−\mathrm{cos}\:\theta\right)}{{R}}−\mathrm{2}\omega\:\mathrm{cos}\:\theta\left(\frac{{V}}{{R}}\right)+\left(\frac{\mathrm{3}{M}}{\mathrm{2}{m}}+\mathrm{1}\right)\left(\frac{{V}}{{R}}\right)^{\mathrm{2}} =\mathrm{0} \\ $$$$\Rightarrow\frac{{V}}{{R}}=\frac{\omega\:\mathrm{cos}\:\theta+\sqrt{\omega^{\mathrm{2}} \left(\mathrm{cos}^{\mathrm{2}} \:\theta−\mu\right)+\frac{\mathrm{2}\mu{g}\left(\mathrm{1}−\mathrm{cos}\:\theta\right)}{{R}}}}{\mu}\: \\ $$$${with}\:\mu=\frac{\mathrm{3}{M}}{\mathrm{2}{m}}+\mathrm{1} \\ $$$$\frac{\omega{ds}}{{Rd}\theta}=\frac{\omega\:\mathrm{cos}\:\theta+\sqrt{\omega^{\mathrm{2}} \left(\mathrm{cos}^{\mathrm{2}} \:\theta−\mu\right)+\frac{\mathrm{2}\mu{g}\left(\mathrm{1}−\mathrm{cos}\:\theta\right)}{{R}}}}{\mu} \\ $$$$\frac{{ds}}{{d}\theta}={R}×\frac{\mathrm{cos}\:\theta+\sqrt{\mathrm{cos}^{\mathrm{2}} \:\theta−\mu+\frac{\mathrm{2}\mu{g}\left(\mathrm{1}−\mathrm{cos}\:\theta\right)}{{R}\omega^{\mathrm{2}} }}}{\mu} \\ $$$$\Rightarrow{s}={R}\int_{\mathrm{0}} ^{\theta} \frac{\mathrm{cos}\:\theta+\sqrt{\mathrm{cos}^{\mathrm{2}} \:\theta−\mu+\frac{\mathrm{2}\mu{g}\left(\mathrm{1}−\mathrm{cos}\:\theta\right)}{{R}\omega^{\mathrm{2}} }}}{\mu}{d}\theta \\ $$$${a}_{{x}} =\frac{{dv}_{{x}} }{{dt}}=\frac{\omega{d}}{{d}\theta}\left({V}−{R}\:\mathrm{cos}\:\theta\:\omega\right)=\omega\left(\frac{{dV}}{{d}\theta}−{R}\mathrm{cos}\:\theta\:\frac{{d}\omega}{{d}\theta}+{R}\:\mathrm{sin}\:\theta\:\omega\right) \\ $$$${a}_{{y}} =\frac{{dv}_{{y}} }{{dt}}=\frac{\omega{d}}{{d}\theta}\left(−{R}\:\mathrm{sin}\:\theta\:\omega\right)=\omega\left(−{R}\:\mathrm{sin}\:\theta\:\frac{{d}\omega}{{d}\theta}−{R}\:\mathrm{cos}\:\theta\:\omega\right) \\ $$$${ma}_{{x}} =−{N}\:\mathrm{sin}\:\theta \\ $$$${m}\omega\left(\frac{{dV}}{{d}\theta}−{R}\mathrm{cos}\:\theta\:\frac{{d}\omega}{{d}\theta}+{R}\:\mathrm{sin}\:\theta\:\omega\right)=−\frac{\mathrm{3}{M}}{\mathrm{2}}×\frac{\omega{dV}}{{d}\theta} \\ $$$$\Rightarrow\mu\frac{{d}}{{d}\theta}\left(\frac{{V}}{{R}}\right)−\mathrm{cos}\:\theta\:\frac{{d}\omega}{{d}\theta}+\mathrm{sin}\:\theta\:\omega=\mathrm{0} \\ $$$${ma}_{{y}} ={N}\:\mathrm{cos}\:\theta−{mg} \\ $$$${m}\omega\left(−{R}\:\mathrm{sin}\:\theta\:\frac{{d}\omega}{{d}\theta}−{R}\:\mathrm{cos}\:\theta\:\omega\right)=\frac{\mathrm{3}{M}}{\mathrm{2}\:\mathrm{sin}\:\theta}×\frac{\omega{dV}}{{d}\theta}\:\mathrm{cos}\:\theta−{mg} \\ $$$$\Rightarrow\frac{\mathrm{3}{M}}{\mathrm{2}{m}}×\frac{{d}}{{d}\theta}\left(\frac{{V}}{{R}}\right)=\frac{{g}}{\omega{R}}−\left(\mathrm{sin}\:\theta\:\frac{{d}\omega}{{d}\theta}+\mathrm{cos}\:\theta\:\omega\right)\mathrm{tan}\:\theta \\ $$$$\frac{\mathrm{3}{M}}{\mathrm{2}{m}\mu}\mathrm{cos}\:\theta\:\frac{{d}\omega}{{d}\theta}−\frac{\mathrm{3}{M}}{\mathrm{2}{m}\mu}\mathrm{sin}\:\theta\:\omega=\frac{{g}}{\omega{R}}−\frac{\mathrm{sin}^{\mathrm{2}} \:\theta}{\mathrm{cos}\:\theta}\:\frac{{d}\omega}{{d}\theta}−\mathrm{sin}\:\theta\:\omega \\ $$$$\begin{array}{|c|}{\left(\frac{\mathrm{3}{M}}{\mathrm{3}{M}+\mathrm{2}{m}}+\mathrm{tan}^{\mathrm{2}} \:\theta\right)\mathrm{cos}\:\theta\:\frac{{d}\omega}{{d}\theta}−\left(\frac{\mathrm{2}{m}}{\mathrm{3}{M}+\mathrm{2}{m}}\right)\mathrm{sin}\:\theta\:\omega−\frac{{g}}{\omega{R}}=\mathrm{0}}\\\hline\end{array} \\ $$$${solve}\:{this}\:{d}.{e}.\:\left({hard}\:{to}\:{do}!\right){for}\:\omega={f}\left(\theta\right)\: \\ $$$${under}\:\omega=\mathrm{0}\:{at}\:\theta=\mathrm{0} \\ $$$$……. \\ $$$${once}\:{we}\:{have}\:\omega={f}\left(\theta\right),\:{we}\:{also}\:{get}\:\frac{{V}}{{R}}. \\ $$$${from}\:\frac{{d}}{{d}\theta}\left(\frac{{V}}{{R}}\right)=\mathrm{0}\:{we}\:{get}\:\theta_{\mathrm{1}} \:{at}\:{which}\:{the} \\ $$$${small}\:{ball}\:{loses}\:{contact}\:{to}\:{cylinder}. \\ $$$${we}\:{also}\:{get}\:{the}\:{v}_{{x}} \:{and}\:{v}_{{y}} \:{at}\:{this}\:{instant}. \\ $$$${upon}\:{now}\:{the}\:{small}\:{ball}\:{has}\:{the} \\ $$$${motion}\:{of}\:{projectile}\:{and}\:{we}\:{can}\:{find} \\ $$$${the}\:{position}\:{where}\:{it}\:{hits}\:{the}\:{ground}. \\ $$
Commented by mr W last updated on 23/Dec/21
$${that}'{s}\:{the}\:{point}\:{i}\:{can}\:{maximally}\:{come} \\ $$$${to}. \\ $$
Commented by Tawa11 last updated on 23/Dec/21
$$\mathrm{Great}\:\mathrm{sir} \\ $$
Commented by ajfour last updated on 23/Dec/21
$${mg}\left(\mathrm{2}{R}\right)=\frac{\mathrm{1}}{\mathrm{2}}\left(\frac{{mR}^{\mathrm{2}} }{\mathrm{2}}\right)\omega^{\mathrm{2}} +\frac{\mathrm{1}}{\mathrm{2}}{m}\left({v}_{{x}} ^{\mathrm{2}} +{v}_{{y}} ^{\mathrm{2}} \right) \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:+{mgR}\left(\mathrm{1}+\mathrm{cos}\:\theta\right)\:\:\:…\left({i}\right) \\ $$$$\:\:\:\:\:\:\:\:\:\left({energy}\:{conservation}\right) \\ $$$${mv}_{{x}} ={m}\omega{R}\:\:\:\:\left({linear}\:{momentum}\:\right. \\ $$$$\left.\:\:\:\:\:\:\:\:\:\:\:\:\:\:..\left({ii}\right)\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:{conservation}\right) \\ $$$${mx}={ms}\:\:\:..\left({iii}\right)\:\:\:\:\left({center}\:{of}\:{mass}\:\right) \\ $$$$\left.\mathrm{2}\left.{s}={R}\mathrm{cos}\:\theta\:\:..\right){iv}\right) \\ $$$${mv}_{{x}} {R}\left(\mathrm{1}+\mathrm{cos}\:\theta\right)+{mv}_{{y}} {x} \\ $$$$\:\:\:\:\:\:\:\:\:\:\:=\frac{{mR}^{\mathrm{2}} }{\mathrm{2}}\omega+{mR}^{\mathrm{2}} \omega\:\:\:…\left({v}\right) \\ $$$$\left({angular}\:{momentum}\:{conservation}\right) \\ $$$${now}\:\:\:{v}_{{y}} {t}+\frac{\mathrm{1}}{\mathrm{2}}{gt}^{\mathrm{2}} ={R}\left(\mathrm{1}+\mathrm{cos}\:\theta\right)\:..\left({vi}\right) \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:{v}_{{x}} {t}=\left({b}−{x}\right)\:\:\:..\left({vii}\right) \\ $$$$\:\:\:………………………………………… \\ $$$${so}\:\:\:{v}_{{x}} =\omega{R} \\ $$$$\left({b}−\frac{{R}\mathrm{cos}\:\theta}{\mathrm{2}}\right)\left(\frac{{v}_{{y}} }{\omega{R}}\right)+\frac{\mathrm{1}}{\mathrm{2}}\frac{{g}}{\omega^{\mathrm{2}} {R}^{\mathrm{2}} }\left({b}−\frac{{R}\mathrm{cos}\:\theta}{\mathrm{2}}\right)^{\mathrm{2}} \\ $$$$\:\:={R}\left(\mathrm{1}+\mathrm{cos}\:\theta\right) \\ $$$${say}\:\:\frac{{b}}{{R}}=\lambda\:\:\:;\:\:\frac{{v}_{{y}} }{\omega{R}}=\mu \\ $$$$\mathrm{4}\left(\mathrm{2}\lambda−\mathrm{cos}\:\theta\right)\mu+\frac{{g}}{\omega^{\mathrm{2}} {R}}\left(\mathrm{2}\lambda−\mathrm{cos}\:\theta\right)^{\mathrm{2}} \mu^{\mathrm{2}} \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:\:=\mathrm{8}\left(\mathrm{1}+\mathrm{cos}\:\theta\right)\:\:\:\:\:…..\left({A}\right) \\ $$$$\:\:\lambda\:=?\:\:\:\left({so}\:{we}\:{need}\:\:\:\mu\:{and}\:\mathrm{cos}\:\theta\right) \\ $$$${and}\:{from}\:..\left({v}\right) \\ $$$$\mathrm{2}\left(\mathrm{1}+\mathrm{cos}\:\theta\right)+\mu\mathrm{cos}\:\theta=\mathrm{3} \\ $$$$\Rightarrow\:\:\mathrm{cos}\:\theta=\frac{\mathrm{1}}{\mathrm{2}+\mu} \\ $$$${And}\:{from}\:..\left({i}\right) \\ $$$$\frac{\mathrm{8}{g}}{{R}}=\omega^{\mathrm{2}} +\mathrm{2}\omega^{\mathrm{2}} \left(\mathrm{1}+\mu^{\mathrm{2}} \right)+\frac{\mathrm{4}{g}}{{R}}\left(\mathrm{1}+\mathrm{cos}\:\theta\right) \\ $$$$\Rightarrow\:\:\omega^{\mathrm{2}} =\frac{\mathrm{4}{g}}{{R}}\left(\frac{\mathrm{1}−\mathrm{cos}\:\theta}{\mathrm{3}+\mathrm{2}\mu^{\mathrm{2}} }\right)\:\:\:…\left({I}\right) \\ $$$$\Rightarrow\:\: \\ $$$$\omega^{\mathrm{2}} {R}=\mathrm{4}{g}\left(\frac{\mathrm{1}−\frac{\mathrm{1}}{\mathrm{2}+\mu}}{\mathrm{3}+\mathrm{2}\mu^{\mathrm{2}} }\right) \\ $$$${also}\:\:\:\:\:\left(\mathrm{2}\omega{R}\mathrm{cos}\:\theta\right)^{\mathrm{2}} +\left(\mu\omega{R}\mathrm{sin}\:\theta\right)^{\mathrm{2}} \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:\:\:={gR}\mathrm{cos}\:\theta \\ $$$$\Rightarrow\:\omega^{\mathrm{2}} =\:\frac{{g}}{{R}}\left(\frac{\mathrm{cos}\:\theta}{\mathrm{4cos}\:^{\mathrm{2}} \theta+\mu^{\mathrm{2}} \mathrm{sin}\:^{\mathrm{2}} \theta}\right)\:\:..\left({II}\right) \\ $$$${from}\:\:…\left({I}\right)\:\&\:\left({II}\right) \\ $$$$\mathrm{4}\left(\mathrm{1}−\mathrm{cos}\:\theta\right)\left(\mathrm{4cos}\:^{\mathrm{2}} \theta+\mu^{\mathrm{2}} \mathrm{sin}\:^{\mathrm{2}} \theta\right) \\ $$$$\:\:\:\:\:=\mathrm{cos}\:\theta\left(\mathrm{3}+\mathrm{2}\mu^{\mathrm{2}} \right) \\ $$$${but}\:\:\mathrm{cos}\:\theta=\frac{\mathrm{1}}{\mathrm{2}+\mu} \\ $$$${hence}\:{we}\:{obtain}\:\boldsymbol{\mu}\:{from} \\ $$$$\mathrm{4}\left(\mathrm{1}−\frac{\mathrm{1}}{\mathrm{2}+\mu}\right)\left\{\left(\frac{\mathrm{2}}{\mathrm{2}+\mu}\right)^{\mathrm{2}} +\frac{\mu^{\mathrm{2}} }{\mathrm{1}−\frac{\mathrm{1}}{\left(\mathrm{2}+\mu\right)^{\mathrm{2}} }}\right\} \\ $$$$\:\:\:\:\:\:=\left(\frac{\mathrm{3}+\mathrm{2}\mu^{\mathrm{2}} }{\mathrm{2}+\mu}\right) \\ $$$${and}\:{now}\:\:{eq}..\left({A}\right)\:\:\:\:{gives}\:{us}\:\lambda=\frac{{b}}{{R}} \\ $$$$ \\ $$$$ \\ $$
Commented by mr W last updated on 23/Dec/21
$${great}! \\ $$$${i}\:{need}\:{some}\:{time}\:{to}\:{follow}\:{it}. \\ $$$${i}\:{think}\:{with}\:\omega\:{you}\:{don}'{t}\:{mean} \\ $$$$\omega=\frac{{d}\theta}{{dt}},\:{right}? \\ $$
Commented by ajfour last updated on 23/Dec/21
$${yeah}\:{its}\:{not}\:\frac{{d}\theta}{{dt}}\:,\:{its}\:{the}\:{angular} \\ $$$${velocity}\:{of}\:{rotation}\:{of}\:{the}\:{cylinder}. \\ $$