Solving Yo-Yo Force Problem: Find Acceleration & Friction Force

[Ruitker]

Homework Statement

A yoyo of mass m=2 kg and moment of inertia ICM=0.0625 kg m2 consists of two solid disks of radius R=0.25 m, connected by a central spindle of radius r=0.1875 m and negligible mass. A light string is coiled around the central spindle. The yoyo is placed upright on a flat rough surface and the string is pulled with a horizontal force F=28 N, and the yoyo rolls without slipping.
The force is applied at the top of the spindle; so above the center of mass.

Find the acceleration of the yo-yo.
Find the frictional force

Homework Equations

F-fr=ma
Tq=I*alpha

The Attempt at a Solution

I started taking moments about the centre of mass, which came to R*fr - r*F = Torque
Then equated this with the Inertia and alpha.
R*fr - r*F = I*alpha
Then changed alpha to a/R.
So ended up with a = ((R*fr - r*F)*R)/I
I then use the F-fr=ma equation to solve for both fr and a.
The answers i get are incorrect.

 

[ehild]

Homework Statement

A yoyo of mass m=2 kg and moment of inertia ICM=0.0625 kg m2 consists of two solid disks of radius R=0.25 m, connected by a central spindle of radius r=0.1875 m and negligible mass. A light string is coiled around the central spindle. The yoyo is placed upright on a flat rough surface and the string is pulled with a horizontal force F=28 N, and the yoyo rolls without slipping.
The force is applied at the top of the spindle; so above the center of mass.

Find the acceleration of the yo-yo.
Find the frictional force

Homework Equations

F-fr=ma
Tq=I*alpha

The Attempt at a Solution

I started taking moments about the centre of mass, which came to R*fr - r*F = Torque

Are you sure the torque of the friction acts against the torque of the applied force?

Then equated this with the Inertia and alpha.
R*fr - r*F = I*alpha
Then changed alpha to a/R.
So ended up with a = ((R*fr - r*F)*R)/I
I then use the F-fr=ma equation to solve for both fr and a.
The answers i get are incorrect.

ehild