Kinematic problem, are my variables right,

[rashad764]

I simply used $t$ for the elapsed time which is fairly common practice, whereas your professor is having you use $t_2-t_1$. It means the same thing, but your professor's notation is not unusual either.

lets say i was trying to do t2-t1 for x2 and and x1. so 2.5-6=-3.5. how does that work

 

[MarkFL]

lets say i was trying to do t2-t1 for x2 and and x1. so 2.5-6=-3.5. how does that work

I'm not sure what you're asking here, but $t$'s represent time and $x$'s represent distance or position, so you don't want to interchange them.

 

[rashad764]

I'm not sure what you're asking here, but $t$'s represent time and $x$'s represent distance or position, so you don't want to interchange them.

in this problem, what would be the time at position 2 and at position 1

 

[MarkFL]

in this problem, what would be the time at position 2 and at position 1

For the first phase of the problem, we could let:

$t_1=0\text{ s},\,t_2=6\text{ s}\implies t=\Delta t=v_2-v_1=6\text{ s}$

$x_1=0\text{ m},\,x_2=77.4\text{ m}\implies x=\Delta x=x_2-x_1=77.4\text{ m}$

 

[rashad764]

thanks for helping, really appreciate it!