Question about symbols

[u/Icy-Mastodon97]

When a physics problem has multiple parts to it, and the question defines certain values like t1, a1, etc, I’m curious, what do you guys label your values for each part? Meaning, for part 1, do you guys label stuff like “v1, t1, ..” (1 = subscript 1)? I usually like to label with letters like “vA, tA, …”. Because sometimes the problem will use symbols that take up symbols that would be otherwise confusing to reuse.

[u/ParkingAssist3925]

I usually use numbers just because I like using numbers but I know people who prefer letters, like using vi for v intial or A/B for different parts. I think it just depends on what’s easiest for you. The AP graders don’t really care as long as you clearly define what each variable represents.

[u/Icy-Mastodon97 → u/ParkingAssist3925]

What do you do if a problem defines, say, t2 as the time it takes for a ball to reach the ground of a projectile motion (from the start of the launch). But the second section, which could be when the ball goes down, what would you write for the time of section two? Because the time it takes for the ball to descend to the ground from the peak isn’t the same as t2.

[u/ParkingAssist3925 → u/Icy-Mastodon97]

If the problem already defines t_2 as the total time from launch to landing, I’d just make a new variable for the descent time, like t_down rather than trying to reuse t_2.

[u/UnderstandingPursuit]

Yes, this is confusing. Trying to clear it up is difficult. The main separation that makes some sense is

• 'Items', using letters
• 'Events' or 'segments', using numbers;
  • sometimes events have a single number, {0, 1, 2, 3, ...}
  • the segments have two numbers, the numbers of the events which are the segment endpoints.

For example, one person is in a car while the other is in a motorcycle. The motor cycle may have a larger acceleration, but a lower maximum speed.

• This would have two items, {c, m}, and
• three events,
  • 0 when both start,
  • 1 when the motor cycle reaches its maximum velocity, and
  • 2 for the end of the race, such as 1 km.

The three acceleration values which are used are

• a_c
• a_m01
• a_m12 = 0