Basic dynamics/acceleration question

1. The problem statement, all variables and given/known data

A 1000kg car is travelling at 27.0 m/s. Determine the force required to stop it in 70.0 m.

3. The attempt at a solution

I attempted to treat this question as if I knew how many seconds it took to stop, and did this:

70.0m / 27.0m/s = 2.59259s

2.59259s / 27.0m/s = 0.096

1000kg / 0.096 = 10414.29N

F = 10.4kN

But then I realized that this is all predicated on the idea that we are moving at 27.0 m/s throughout the whole 70.0m rather than accelerating. Now I have no idea what to do, and both of my textbooks are proving useless. Please help, and sorry if the question is messed up or hard to decipher, this is my first post.

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