Rotational Motion Homework: K1+U1=K2+U2

[Muath Mushtaha]

Homework Statement

http://serv1.gulfup.cc/i/00003/ev7u8r04c18k.jpg

Homework Equations

K1+U1=K2+U2

The Attempt at a Solution

I have the solution i am just confused about one point,
in the solution, it considred both the translational and rotational kinetic energy for the cylinder on the tabletop,
but since the table is frictionless and the string is attached to its center, shouldn't it not rotate, thus only have translational energy and not rotational energy?

 

[gneill]

Homework Statement

http://serv1.gulfup.cc/i/00003/ev7u8r04c18k.jpg

Homework Equations

K1+U1=K2+U2

The Attempt at a Solution

I have the solution i am just confused about one point,
in the solution, it considred both the translational and rotational kinetic energy for the cylinder on the tabletop,
but since the table is frictionless and the string is attached to its center, shouldn't it not rotate, thus only have translational energy and not rotational energy?

The problem states that the cylinder rolls without slipping. That means that the table surface is not frictionless.

 

[croad]

It clearly states that the cylinder does not slip, essentially the distance traveled is only by rolling. So just consider the rotational motion.

 

[theodoros.mihos]

Frictionless are mechanical parts.