Question

Figure shows three identical yo-yos initially at rest on a horizontal surface. For each yo-yo the string is pulled in the direction shown. In each case there is sufficient friction for the yo-yo to roll without slipping. Draw a free-body diagram for each yo-yo. In what direction will each yo-yo rotate?

Answer 1

Hint
To draw the free body diagram, we need to draw all the forces that are acting on the yo-yo. The sum of all these forces will give us the net force and from there we can find the net torque. The direction of the net torque gives the direction in which the yo-yo rotates.

Complete step by step answer
The free body diagrams are drawn by considering all the forces that are acting on the yo-yo. So the free body diagram of the first yo-yo is given by the following diagram.

The point of contact of the yo-yo on the ground will be the point through which the axis passes. So the force exerted on the yo-yo will produce a net anti-clockwise torque. Due to this the yo-yo will rotate in the anti-clockwise direction.
For the second case, the free body diagram is given by,

In this case also as the previous one, the force on the yo-yo will produce a clockwise torque and due to this the yo-yo will have a clockwise motion.
For the third case the free body diagram will be as follows,

In this case also the force on the yo-yo will produce a clockwise torque and due to this the yo-yo will have a clockwise motion.
Therefore, the yo-yo will have clockwise motion in the second and third case and anti-clockwise motion in the first case.

Note
Free body diagrams in physics are used to visualize the applied forces and the resulting actions on a body due to those forces. They consist of a simple version of the body and the forces drawn with straight line arrows. And the momenta are drawn with curved lines if necessary to depict the direction of motion of the body.