5:40 AM
Hello @JohnRennie sir
Hi :-)
I searched a lot also worked on equations but didn't find any satisfactory answer.
What minus sign? What equation do you mean?
W = - ∆U
F = - ∆U/∆x
Suppose a system starts with an internal energy U and it does work W.
5:45 AM
Yes
That work has to come from the system's internal energy, so U has to decrease by W i.e. U + W stays constant.
Since U decreases the change ΔU is a negative number, but the work done W is a positive number. So -ΔU is the same as W.
Sir pls don't use thermodynamics , pls use mechanics example. Thanks
That's how we get the first equation.
What I've said above applies to mechanical systems e.g. the system could be a spring and U is the energy stored in the spring.
What about example object moving upward and gravitational force downward.
If I take care of direction of displacement and force in opposite and put cos180, I get accurate result with proper sign. But if I don't put cos180 then I found sign problem.
In example of gravitational potential energy with upward motion.
∆KE = ∆PE Pls use this equation

1 hour later…
7:10 AM
@JohnRennie Hi !
Hi :-)

2 hours later…
9:28 AM
@JohnRennie Hi :)