# Rotational Motion Problem - 11

Hi friends,

The problem is as:

https://fbcdn-sphotos-a-a.akamaihd.net/hphotos-ak-prn2/q71/s720x720/1503374_1461728057387633_909744247_n.jpg

Attempt -

https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-prn2/1506899_1461728417387597_658199054_n.jpg

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haruspex
Homework Helper
Gold Member
a = Rα is for rolling contact.

a = Rα is for rolling contact.
Yes But centre of mass of the sphere woild be going with Translational acceleration,
Whose value would come from the bottom point in contact using, a = rα
Isn't it?

haruspex
Homework Helper
Gold Member
Yes But centre of mass of the sphere woild be going with Translational acceleration,
Whose value would come from the bottom point in contact using, a = rα
Isn't it?
No, as I said, that's only for rolling contact. When the spinning cylinder is placed on the plank it will skid at first. Suppose frictional force is F. What linear acceleration will that produce? What torque? What angular acceleration?

No, as I said, that's only for rolling contact. When the spinning cylinder is placed on the plank it will skid at first. Suppose frictional force is F. What linear acceleration will that produce? What torque? What angular acceleration?
https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-ash4/1506955_1462163254010780_1540770628_n.jpg

haruspex
Homework Helper
Gold Member
That's all correct, but what you are asked for is a. Your remaining step is to figure out what f is in terms of m, g and mu.

That's all correct, but what you are asked for is a. Your remaining step is to figure out what f is in terms of m, g and mu.
Well, here a is f/m and f will be, μmg/m = µg(i)
and acceleration of plank would be µg(-i)

so acceleration of sphere w.r.t. plank would be 2µg.

Is that correct?

haruspex
Homework Helper
Gold Member
Well, here a is f/m and f will be, μmg/m = µg(i)
and acceleration of plank would be µg(-i)

so acceleration of sphere w.r.t. plank would be 2µg.

Is that correct?
That's it. You didn't need to worry about the rotations at all!