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Carly H.

asked • 06/05/20

Mrs. Baker is driving her Ford Fiesta at a rate of 70 mi/hr. What is her acceleration if it takes her 4 seconds to come to a complete stop?

a = vf – vi vf = vi + at t = vf-vi

          t     a    

these are the formulas i was given im not sure which one to use or even how to do this.

Find the acceleration

Ronn K.

When answering any question, in math or in any other subject, first make sure you know what you are being asked for. In this case, you are being asked for acceleration. Secondly, make sure you know what all the variables (letters) stand for. These formulas have an “a,” “t,” “vi” and “vf.” The variable “a” is the acceleration. So the formula that starts “a = “ will be the easiest one if the answer you seek is the acceleration. Note that because your velocity is decreasing, your answer should end up being a negative number (that’s a quick check to make sure you are on the right track). "T" stands for time. “vi” stands for “velocity-initial” (or beginning velocity) and “vf” stands for “velocity final,” (or ending velocity). The formula for computing acceleration (a) tells you that it will be the difference between the two velocities, divided by the time it takes to make that change in velocity. Vf here is 70 because that’s the velocity you start at. A complete stop is velocity 0 (you are not moving), so vf=0. And the time it takes to go from 70 to 0 is 4 seconds (t). And if you subtract vi from vf you get -70. Then divide by 4 (t) and you get -17.5. Your acceleration is decreasing at 17.5 mi/hr. Or a = -17.5.


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