A sprinter explodes out of the starting block with an acceleration of +3.5 m/s2, which she sustains for 0.8 s. Then, her acceleration drops to zero for the rest of the race. (a) What is her velocity at t = 0.8 s.

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.
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SOLVED:A sprinter explodes out of the starting block with an ...
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