BBC Focus Magazine

[jpYB3Gq]

Couldn't help it. One more example:

Eg 3: (Mechanics) Galileo drops an iron ball from the Power of Pisa. delta( potential energy) < 0 and delta( kinetic energy) > 0 and delta (total mechanical energy) = 0.
Of course you can equally say the opposite is true, delta( potential energy) < 0 and delta (kinetic energy) < 0, provided you also say delta(time)<0, but this is really absurd. Because you are saying the reverse is true, because the ball is traveling backward in time ie time travel.

Esther: my exam papers are marked by Cambridge in 1983 and 1985. Perhaps it is the era or subject, but not the country.

[The Beige Avenger]

.....
Eg 3: (Mechanics) Galileo drops an iron ball from the Power of Pisa. ......

This is wrong!

The Power of Pisa is a never ending source of mystical energy that certain superheroes draw forth their strength from.

Not to be confused with the Tower of Pisa which is just a wonky building.

I'm really concerned about this as a lot of students are going to end up thinking Galileo was some kind of mystic...

</pisstake>

You start a problem in physics by thinking about the boundary conditions of the system in question and then defining them, for example t=0 s and t=60 s could equal start and stop respectively, once you've done that you just need to remember the boundaries.
It's common sense to use "end-start" as jp says as we usually take t=0 to be the beginning of the system but we could easily take the end point and get the same answer.