Work done on vs by systems

[mspeedwagon]

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I think I've managed to completely confuse myself and am hoping someone can help.

Say you were moving a box horizontally (no friction), is the work done ON the system positive or negative? (I said it was positive b/c force is applied in the direction of motion, but not sure).

Does the energy of the system increase or decrease?

Work done by the box... is it positive or negative?

A link that explains this well would be appreciated too.

 

[MedPR]

I think I've managed to completely confuse myself and am hoping someone can help.

Say you were moving a box horizontally (no friction), is the work done ON the system positive or negative? (I said it was positive b/c force is applied in the direction of motion, but not sure).

Does the energy of the system increase or decrease?

Work done by the box... is it positive or negative?

A link that explains this well would be appreciated too.

As always with work, it depends what you define as your system.

If work is done on the system, energy is gained and thus deltaE is positive.
If work is done by the system, energy is lost and thus deltaE is negative.

If you define the box as your system, then work is being done on the box and the box is gaining energy.

 

[LoLCareerGoals]

Box is increasing in speed isn't it? If yes, so Ek of the box is obv increasing, so work must be done on the box. Since the motion is horizontal Ep stays the same.