Question

in STP?

3. What would be the value of work done against gravity if a person in a corner had a suitcase

hanging vertically with the ground and walked along the horizontal plane?
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Answer 1

Answer:

Explanation:

The formal definition of work is

W=F.s

Where the dot product indicates that only the component of the force that acts in the same direction as the displacement contributes to work.

Now, the simplified version of Newton's Second Law states that F=m.a

In effect, the displacement and the acceleration or atleast some components of them need to be collinear to have non-zero work.

So when you lift up a suitcase, yes you do work.

When you start to walk forward from rest after that, you accelerate, as does the suitcase in your hand. The force that provides this acceleration is the horizontal component of the reaction force from your leg, and that force does work.

However, what makes the suitcase move with the rest of your body? There has to be a force at the zone of contact with the suitcase and your body that transfers the reaction force to the suitcase, right? And as far as the suitcase is concerned this firce is the only one it sees. This force is contact friction.

So, you have a force acting on an object accelerating it in the same direction as it is acting. This force does work on the suitcase, even when you have no bumps on the surface.