If the external world does work on the system, the quantity of work is negative or positive? I said it was positive and Bob Pursley said I was right, but a Physics student said that it is negative. Please help if you can..
Negative
To determine whether the quantity of work done on a system by the external world is positive or negative, we need to understand how work is defined in physics.
In physics, work is defined as the transfer of energy that occurs when a force is applied to an object and it displaces in the direction of the force. Mathematically, work (W) is calculated as the product of the force (F) applied to an object and the displacement (d) of the object in the direction of the force:
W = F * d * cos(theta)
where theta is the angle between the direction of the force and the direction of displacement.
Now, let's consider your question regarding the external world doing work on the system. If the force applied by the external world and the displacement are in the same direction (theta = 0), then the work done is positive.
On the other hand, if the force applied by the external world and the displacement are in opposite directions (theta = 180 degrees), then the work done is negative.
Therefore, whether the quantity of work is positive or negative depends on the angle between the force and the displacement. If the external world applies a force in the same direction as the displacement of the system, the work done is positive. If the force and displacement are in opposite directions, the work done is negative.
It is worth noting that different sources or individuals may use different conventions or sign conventions for work. Hence, when discussing work, it is important to clarify the conventions and sign conventions being used to avoid confusion and misconception.