A worker with spikes on his shoes pulls on rope that is attached to a box that is resting on a flat, frictionless frozen lake. The box has mass m, and the worker pulls with a constant tension T at an angle θ = 30° above the horizontal. Draw a free-body diagram for this system, assuming that the box moves to the right.

In order to draw a free-body diagram for the given situation, you have to include in the drawing of the box all the forces acting in the box, in the correct directions.

The forces involved are:

The weight force (Let W represent it). This force is produced by the gravity force on the box, its direction is perperdicular to the ground, pointing down.

The normal force (Let N represent it). This force is produced by the contact force that the frozen lake applies to the box, its direction is perperdicular to the lake, pointing up.

The tension force (Let T represent it). This force is produced by the worker, who is pulling the rope. Its direction forms 30° above the horizontal, pointing to the right (because the box moves to right)

Notice that there isn't a friction force because the lake is frictionless. Also notice that the tension produces the movement of the box to the right.