Minimum stopping distance for 6000 kg steel load on truck

[emily69_420]

I am having a huge problem with this physics problem...I just can't figure it out. Please help me if you can.
Heres the problem:
A load of steel with a mass of 6000 kg rests on a flatbed of a truck. It is held in place by metal brackets that can exert a maximum horizontal force of 8000 N. When the truck is traveling 20 m/s, what is the minimum stopping distance if the load is not to slide foreward into the cab?

 

[ZapperZ]

We have a Homework/School work section. Please use it.

Zz.

 

[Päällikkö]

F = ma
$$a_{avg}=\frac{\Delta v}{\Delta t}$$