SOLUTION: If it takes 144ft to stop a car going 60mph, how many feet does it take to stop a car going 45mph?

Algebra ->  Customizable Word Problem Solvers  -> Misc -> SOLUTION: If it takes 144ft to stop a car going 60mph, how many feet does it take to stop a car going 45mph?      Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


   



Question 691134: If it takes 144ft to stop a car going 60mph, how many feet does it take to stop a car going 45mph?
Answer by pmatei(79) About Me  (Show Source):
You can put this solution on YOUR website!
Because you do not know how long it takes to stop the car going 60mph, you need to use this equation:
v%5Bf%5D%5E2+=+v%5Bi%5D%5E2+%2B+2ad
where v%5Bi%5D+=+60+mph+=+60%2A5280+ft%2Fhr, v%5Bf%5D+=+0, and d+=+144ft
0 = 100,362,240,000 ft^2/hr^2 + (288 ft)a
a = - (100,362,240,000 ft^2/hr^2)/(288 ft) = 348480000 ft/hr^2
For the second car assume the same acceleration that you just calculated, but this time v%5Bi%5D+=+45mph+=+45%2A5280+ft%2Fhr and you calculate d:
0 = 56,453,760,000 ft^2/hr^2 - (696960000 ft/hr^2)d
d = (56,453,760,000 ft^2/hr^2)/(696960000 ft/hr^2) = 81 ft