Understanding Work Homework: Does System Do Work on Environment?

[merzperson]

Homework Statement

The kinetic energy of a system decreases while its potential energy and thermal energy are unchanged. Does the environment do work on the system, or does the system do work on the environment?

Homework Equations

W = K1 - K2

The Attempt at a Solution

I got the answer to this question wrong, so I'm having trouble understanding exactly what's going on here (as usual the textbook is of no help, and we didn't cover this explicitly in class...).

Here is what sense I can make in my head, but I just want to make sure I am not making anything up:

The kinetic energy decreases, so we know the final K (K2) is less than the initial K (K1):
W = K1 - K2 and K1 > K2 so W > 0
Since W is positive, the system does work on the environment.

Is this correct logic? How would you have approached the problem? Thanks!

 

[Redbelly98]

Looks good.

Another way to think about it: the system lost energy. That energy had to go somewhere, since energy is conserved. The system lost energy by doing work on the environment.

 

[kerimek]

Your logic is correct. The decrease in kinetic energy implies that work is being done on the system, since work is defined as the change in kinetic energy. In this case, the work is being done by the environment on the system, as the system is losing energy. This could be due to external forces acting on the system, such as friction or air resistance, which are considered to be work done by the environment. Additionally, the fact that the potential and thermal energies remain unchanged suggests that no work is being done by the system itself. Overall, your understanding of the situation is correct and your approach to the problem is sound.