Which will reach the bottom faster: solid or hollow sphere?

[Milo Martian]

I think is better to do an Energy balance...
https://www.physicsforums.com/attachments/104346

But won't mechanical energy change due to friction? just curious

 

[llober]

But won't mechanical energy change due to friction? just curious

If there's no sliding, there's no loss by friction, because the no sliding translates into speed zero at the contact point, so the "friction force" does not move.

 

[Milo Martian]

If there's no sliding, there's no loss by friction, because the no sliding translates into speed zero at the contact point, so the "friction force" does not move.

OK

 

[haruspex]

Okay, i got it .
F_ext= mgsinA - f= ma_cm ...(1)
fXR= torque = I X angular acc. = I X a_cm/R
=> f= Ia_cm/R² ...(2)
From (1) and (2) :
ma_cm = mgsinA - Ia_cm/R²
=> a_cm= mgsinA/(m + I/R²)
So, since I_{solid sphere}< I_{hollow sphere}
Therefore, a_cm for solid sphere> a_cm for hollow sphere.
i hope i am right. phew

You got it.