and (b) at the end of the race?

Use the equation of motion v =  u + at for finding out both the parts a and b.

v is the final velocity, u is the initial velocity a is the acceleration and t is the time.

a) The initial velocity of the sprinter is zero, so u = 0, a = 3.5 \frac{m}{s^{2}} and t = 0.8 s.

Plugging these in the equation we have her velocity for 8 sec as

v\ =\ 0\ +\ 2.3\ \frac{m}{s^2}\ \times0.8\ s\ =\ 1.84\ \frac{m}{s}  

b) This velocity will become her initial velocity now. From t = 0.8 s, her acceleration will become zero (given), so her velocity at the end of the race will be,

v\ =\ 1.84\ \frac{m}{s}\ +\ 0\ \times0.8\ s\ =\ 1.84\ \frac{m}{s}

So the velocity will be the same.

I found an answer from www.numerade.com

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