Physics Friction Help!?

Question

A crate containing machine parts sits unrestrained on the back of a flatbed truck traveling along a straight road at a speed of 80 km/hr. The driver applies a constant breaking force and comes to a stop in a distance of 22 m. What is the minimum coefficient of static friction between the crate and the truck bed if the crate is not to slide forward?

Answer 1

first calculate a
22=t*80/3.6-.5*a*t^2
and
0=80/3.6-a*t
solve for a



a=11.22
now use F=m*a to calculate the force on the crate
m*11.22
this is equal to
m*g*µs


µs=11.22/9.81
1.14 which means
the crate will slide since µs>1

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