Here's an excerpt from my textbook:
In the following situations, state whether work is being done, and why or why not.
A) A person carrying a backpack walking across a floor
B) A person shoveling snow across a driveway at a constant speed
The solutions are:
A) No work is being done on the bag because the direction of motion is perpendicular to the direction of force due to gravity
B) Work is being done on the shovel because the direction of motion and the direction of the applied force is the same
I have no issue with situation B, but situation A bothers me. Although I agree that no work is being done by the forces of gravity and the force applied to hold it up, is it not the case that the person is applying a force forward to the bag as they walk, and therefore work is being done by that force? To make things a bit more uniform (since walking is a jerky motion), presuming that the person wearing the bag is riding a bike at a constant speed, that means that they have to apply a force that balances wind resistance.
I might say that since there is no net force there is no work being done, but then situation B would have no work being done as well, since the shovel/snow are moving at a constant speed.
Where did I misread this?