I have a couple of kinematic problems for class, and I'm a bit confused about how to get the answers for them. Learning about displacement, position, kinematics and Newton's 2nd law. We have a bunch of formulas we're working with and applying where appropriate.

-Coasting due west on your bicycle at 8.00m/s you encounter a sandy patch of road 7.20m across. When you leave the sandy patch your speed has been reduced to 6.50m/s. Assuming the bicycle slows with constant acceleration, what was the acceleration in the sandy patch?

initial velocity 8.00m/s, displacement 7.2m, final velocity 6.5m/s, acceleration?

I think the formula I use is Vf^2= Vi^2+2a(deltaX). And switched around its a=Vi^2+2a(deltaX)(square root of Vf)

But this gives me 199.8m/s, which I don't think makes sense. Too big. But I'm not sure what I'm doing wrong.

-Landing with a speed of 115m/s, and traveling due south, a jet comes to rest in 7.00X10^2m. Assuming the jet slows with constant acceleration find the magnitude and direction of its acceleration.

initial velocity 115m/s, displacement 7.00X10^2m, final velocity 0m/s

Similar to the first problem, right?

-A 27.0lb meteorite hit a car leaving a 22.0cm deep dent. If it struck with a speed of 550.0m/s, what was its acceleration, assuming it to be constant?

I think this is a problem involving Newton's 2nd law (acceleration = sum of forces/mass), but I'm not sure and am also a bit unsure how to figure what the "sum of all forces" are.