The best way to prevent cholera is to promote healthy sanitation practices and to filter and treat drinking water sources. Cholera bacterium is usually found in water or food sources that have been contaminated by feces from infected person with cholera. It is mostly found and spread in places with inadequate water treatment, poor sanitation, and inadequate hygiene.
You have to find the acceleration first. so you would use the equation a=Vf-V0/t. This would be 0-20/0.5 which equals to be a=-40. then you plug this in to the force equation wich is F=ma. F=55 x -40. F= -2200