1.

A solid cylinder of mass 'm' rolls without slippling down an inclined plane making an angle θ with the horizontal. The frictional force between the cylinder and the incline is what ?

Answer»

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fk  =  \frac{mg \sin( \alpha ) }{3}

consider α = θ

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EXPLANATION —

Consider α = θ

We KNOW from NLM

That in CASE of linear acceleration in rolling, Force can be written as

mg \sin( \alpha )  - fk = ma

--------(1)

Here,

↪ fk is kinetic friction

↪α is angle of inclination with horizontal

Since this frictional force is also responsible for rotation so we can balance the torque

τ = I @ [Here @ is ANGULAR acceleration ]

⇒r*fk = I @

⇒@ = (r*fk) /I

⇒a / r = (r*fk) /I

⇒fk = a*I/r²

Using equation (1)

mg \sin( \alpha ) -    \frac{aI}{ {r}^{2} }  = ma \\  \\ moment \: of  \: inertia  \: of  \\  cylinder\: (I) =  \frac{1}{2} m {r}^{2}

putting \: above \: we \: will \: get \: this \\ a  = \frac{2}{3} g \sin( \alpha )

Now this value again PUT in eqn (1)

mg \sin( \alpha )  - fk = m( \frac{2}{3} g \sin( \alpha ) )

On solving

fk =  \frac{mg \sin( \alpha ) }{3}

HENCE, the frictional force between the cylinders and the incline is (mgsinα) /3

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