Answer:
Friction
Explanation:
The key and most important external forces that allows a man to push a wheelbarrow is frictional force.
Frictional force is a force that opposes motion and will bring it to a halt.
The reason why motion is possible is due to frictional force.
Without friction, a body will move and continue in motion infinitely. No one will be able to control motion.
- Therefore, frictional force is an external force that will allow a man to push a wheelbarrow.
