Recent content by ChrisBrandsborg

Yeah, but how do we calculate the sliding length? I don't think I have calculated that before. Most of our problems have been rolling without sliding..

Distance is d, but do you mean the height? h = dsinθ

Potential at the top, Kinetic at the bottom (rotational and linear) and thermal energy.

But the in problem a-c we assume that there are no friction, which makes the yoyo- roll with sliding. So we cannot use energy-conservation to calculate ω. How can we then do it?

The Torque comes from the string force, right? But how do we calculate the angular velocity when it rolls and slides? Because then energy isn't conserved?

Ffr = μk⋅Mgsinθ ? (Perpendicular to the normal force and in the direction opposite to the motion)

The friction isn't added before d, so is there angular acceleration even if it is slipping? Yeah, I´ll probably figure it out eventually :) thanks for your help!

in c) "What is the acceleration of the yo-yo? The angular acceleration?", Is that just to trick us into believing that there is an angular acc, but in reality it is = 0?

Okay, but to show that, do I only show what we did with the string length etc.. Don´t I need to show that Στ = 0 → α = 0 → ω = 0

no it´s not :) So that´s the answer to a? But if we had friction in opposite direction of the motion, then it would rotate?

hmm, true.. But then how do we get 10 inches of string in 1 revolution?

Yes, since r < R, 1 revolution won´t take as long time for the smaller disc compared to the bigger?

Conditions: * Point of contact -> not moving * w = v/r (if it is rotating, then w > 0) * There is a torque, which makes the yo-yo rotate. First I thought friction made it rotate, but it is the string tension, right?

But how is this related to problem a, about the conditions? "Is it possible to roll down without slipping on the incline? Why/why not? (Carefully think of the rolling-without slipping conditions)."

Hmm.. but if the yo-yo moves 10 inches, wouldn't we need 10 inches of string as well?