Final answer:
A free-body diagram is a useful tool in analyzing forces acting on an object. In the case of a man pulling a crate with friction involved, the diagram would include several forces such as applied force, normal force, gravity, and frictional force. By analyzing these forces, we can apply Newton's second law to determine the crate's acceleration.
Step-by-step explanation:
A free-body diagram is a useful tool in analyzing forces acting on an object. In the case of a man pulling a crate with friction involved, the free-body diagram would include several forces. These forces would include the applied force by the man, the normal force exerted by the ground on the crate, the force of gravity acting downward, and the frictional force opposing the motion. By analyzing these forces, we can apply Newton's second law to determine the crate's acceleration.