15. A person using a rope and pulley system to lift a heavy object.

Solution:

This diagram illustrates a person using a rope and a single fixed pulley to lift a heavy object (barrel). The force indicated by the vector 'F' shows the direction of the pull. A single fixed pulley changes the direction of the applied force, allowing the person to pull downwards to lift the object upwards.

Answer: A person is using a rope and pulley system to lift a heavy object.