Will you roll with me?

Two rigid uniform cylinders each of mass 50 k g 50kg are placed on a rigid and rough inclined plane at an angle of 3 0 30^{\circ} above the horizontal. A massless string connects the axle of the larger cylinder to the rim of the smaller one. If both of the cylinders roll without slipping, what is the acceleration of the smaller cylinder?

Details and Assumptions

g g is 9.81 m s 2 9.81\frac{m}{s^2}


The answer is 1.962.

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2 solutions

L e t s s a y a c c e l e r a t i o n o f b i g g e r c y l i n d e r i s a 1 a n d a c c e l e r a t i o n o f s m a l l e r c y l i n d e r i s a 2 P U R E R O L L I N G : a 1 = ( 2 R ) α . . . . . ( 1 ) a 2 = ( R ) α . . . . . . ( 2 ) a 1 = 2 a 2 . . . . ( 3 ) f o r c 1 : m g s i n θ T η m g c o s θ = m a 1 f o r c 2 : T + m g s i n θ η m g c o s θ = m a 2 e l i m i n a t i n g T : 2 m g s i n θ 2 η m g c o s θ = 3 m a 2 . . . . . . ( 4 ) T o r q u e a b o u t C . O . M o f b i g g e r c y l i n d e r : η m g c o s θ ( 2 R ) = m ( 2 R ) 2 2 . α η m g c o s θ = m a 2 . . . . . . . ( 5 ) u s i n g ( 4 ) a n d ( 5 ) : 2 m g s i n θ = 5 m a 2 a 2 = 1.962 m s 2 Lets\quad say\quad acceleration\quad of\quad bigger\quad cylinder\quad is\quad { a }_{ 1 }\\ and\quad acceleration\quad of\quad smaller\quad cylinder\quad is\quad { a }_{ 2 }\\ PURE\quad ROLLING:\\ { a }_{ 1 }=(2R)\alpha \quad .....(1)\\ { a }_{ 2 }=(R)\alpha \quad ......(2)\\ { a }_{ 1 }=2{ a }_{ 2 }\quad ....(3)\\ for\quad c-1:\\ mgsin\theta -T-\eta mgcos\theta \quad =\quad m{ a }_{ 1 }\\ for\quad c-2:\\ T+mgsin\theta -\eta mgcos\theta \quad =\quad m{ a }_{ 2 }\\ eliminating\quad T:\\ 2mgsin\theta -2\eta mgcos\theta \quad =\quad 3m{ a }_{ 2 }\quad ......(4)\\ Torque\quad about\quad C.O.M\quad of\quad bigger\quad cylinder:\\ \eta mgcos\theta (2R)\quad =\quad \frac { m{ (2R) }^{ 2 } }{ 2 } .\alpha \\ \eta mgcos\theta \quad =\quad m{ a }_{ 2 }\quad .......(5)\\ using\quad (4)\quad and\quad (5)\quad :\\ 2mgsin\theta \quad =\quad 5m{ a }_{ 2 }\\ { a }_{ 2 }\quad =\quad 1.962\quad \frac { m }{ { s }^{ 2 } }

How did you Know that friction is Limiting ? In Actual You Should have To write friction as unknown ' f ' instead of writing it as Kinetic ! Because friction is Rolling which is not equal to kinetic friction. In-fact f s t a t i c , ( L i m i t i n g ) > f k i n e t i c > f R o l l i n g { f }_{ static,(Limiting) }\quad >{ f }_{ kinetic }\quad >{ f }_{ Rolling } . So Please Kindly Recheck this !

Deepanshu Gupta - 6 years, 5 months ago

I did in the same way!

satvik pandey - 6 years, 5 months ago

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@satvik pandey Could you explain why angular acceleration is the same for both of them?

Dhruva Patil - 6 years, 4 months ago

Smaller cylinder can be taken as winding upwards. Writing torque equation about centre of mass for small cylinder we get - Let the tension in the string be T Therefore , RT + Rmgsin30 = mr^2/2 * (a/r) ........ (1) Writing torque equation about inclined on bigger sphere - 2RT = 3mr^2/2 * (a/2R) 2T = 3ma putting in (1) a = 1.96m/s^2

This question is incomplete as it has to be mentioned that the friction is limiting.

If mentioned, it is Level 3 problem.

jaikirat sandhu - 6 years, 5 months ago

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Nope. I Took The Frictions At Two Contact Points As f1 and f2 and solved the problem correctly

Prakhar Bindal - 5 years, 7 months ago

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