Answer:
gravitational force acting on the piano (piano's weight)
force of Chadwick on the piano
force of the floor on the piano (normal force)
Explanation:
Figure is missing: found it in attachment.
In the figure, we notice that the piano is accelerating along the horizontal direction: this means that there is a net force acting along this direction. This force is prodiced by Chadwick, and it acts in the same direction as the acceleration, so one force is:
force of Chadwick on the piano
Also, every object on Earth experencies the force of gravity, which is also called weight. The weight of the piano acts downward, so a second force is:
gravitational force acting on the piano (piano's weight)
Finally, we notice that the piano is in equilibrium along the vertical direction (no acceleration): this is because there is another force acting opposite to the piano's weight (and with equal magnitude), and this force is the normal force exerted by the floor on the piano:
force of the floor on the piano (normal force)
