Asprinter explodes out of the starting block with an acceleration of +4.2 m/s2, which she sustains for 0.9 s. then, her acceleration drops to zero for the rest of the race. (a) what is her velocity at t = 0.9 s. m/s (b) what is her velocity at the end of the race? m/s

a) 3.78 m/s

b) 3.78 m/s

Explanation:

a )From the equations of kinematics   we know that

     Vf - Vi = at

since Initial speed Vi = 0

acceleration = 4.2 m/s2

so we have

     Vf = a t

           = (4.2) (0.9)

         = 3.78 m/s

velocity at t = 0.9 s. m/s is 3.78 m/s

b) If the sprinter maintains constant velocity then acceleration becomes zero.

   So velocity is 3.78 m/s

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