SOLUTION: With an average acceleration of -2 m/s2, how long will it take to a cyclist to bring a bicycle with an initial speed of 5 m/s to a complete stop?

(a)  If the question is "how long time", then write the basic equation (like definition) of the acceleration

         a = ,


     where "a" is the acceleration, t is the time interval,   and   are the velocities 
     at the beginning and the end of the time interval, respectively.


     Substitute the given values into equation (1)  a = -2 m/s^2,   = 0 m/s (full stop),   = 5 m/s

         -2 = ,  or  -2 = .


     It gives  t =  =  = 2.5 seconds.     ANSWER



(b)  If the question is "how long distance", then use the formula 

         d =  =  =  = 6.25 m.    ANSWER


     Here 2.5 represents 2.5 s, which is the braking time found above.