A sprinter 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