# Homework Help: What cannot be less than zero?

1. Jul 21, 2008

### tinwhistler

1. Work, Power, Weight, and Kinetic energy are all scalar quantaties. Which cannot be less than zero?

2. Relevant definitions
Work is a force action through a distance that is in the direction of the force.
Power is the rate at which work is performed.
Weight is the force exerted on a mass as a force of gravity.
Kinetic energy is the energy (ability to do work) a body or particle posseses because of its motion.

3. The attempt at a solution

Could only find the definitions to assist me. Work can be consumed, so can power, so I'm pretty sure those are not the answer. Then, when there is no movement of particles, there would be no kinetic energy, right? But can there be less than that? Moving backwards? What about weight. It is possible to have an absence of a gravitational force, but can there be less than that? There should only be one answer. I am leaning towards weight, but if someone can clarify for me, and tell me if I'm right, totally wrong, etc, I'd appreciate it.

2. Jul 21, 2008

### fundoo

3. Jul 21, 2008

### PhanthomJay

Weight is a vector quantity, not a scalar. It does not belong in the problem statement.

4. Jul 21, 2008

### stewartcs

The weight of a body is the magnitude of the net force required to prevent the body from falling freely, as measured by someone on the ground.

So the weight would then equal the magnitude of the gravitational force on the body.

$$W = mg$$

Assuming the ground is the inertial reference frame of course. So I believe in this context it should probably be included.

CS

5. Jul 22, 2008

### Hootenanny

Staff Emeritus
I must admit that I have never seen weight defined as a scalar quantity. In all the situations I have met, weight is a vector.

6. Jul 22, 2008

### stewartcs

I'm in agreement with you guys that weight, strictly speaking, is a vector. I was just saying that in the context the question was written (i.e. what cannot be less than zero), since weight is normally defined as the magnitude it can't be negative.

Not sure why I'm trying to justify a question that is obviously written poorly!

CS