Physics: Non uniform motion

I have not done much physics before: I don't get how to do questions that deal with what happened in a particular SECOND
So questions like:

- A stone which is dropped from rest into a mine shaft falls a distance of 24.5 m DURING THE LAST SECOND. Find depth of the shaft

or
- Starting from rest a rocket accelerates at a rate of 4 m/s2. What distance will it travel DURING THE TENTH SECOND

I do not have enough experience with physics to understand these; although i think it can be determined
by just these equations:
a= v2-v1/t
v22 = v12 + 2ad
and
d = v1t + 1/2 at2

In both I guess v1=0, and the distance is given for the first, the acceleration for the second.
Do I also incorporate gravity(9.8 m/s2)? Please tell me how to approach these.

Thanks

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asked by Anne
  1. find when the last second, on the second question, like at t=10 find the distance it has traveled. Then find the same distnace for t=9. The difference in distances is the distance in the last second.

  2. There is another way (calculus differentials) way.
    find ddistance/dt=vi+at at t=start of last second, then use this as the vi for the tenths second. d=vi+at where t is just one second.
    I prefer the first way I illustrated.

  3. thanks!
    but what do i do when the time isnt given like in the first question?

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    posted by Anne
  4. wait.. i didn't get the right answer.
    i got 530 m in the 10th second
    and then 432.9 in the 9th
    subtracted, they give 97.1 but the answer should be 38 m?

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    posted by ella

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