# Physics

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A runner of mass 51.5 kg starts from rest and accelerates with a constant acceleration of 1.35 m/s2 until she reaches a velocity of 5.7 m/s. She then continues running with this constant velocity. (Take the direction the runner is going to be the positive direction. Indicate the direction with the sign of your answer.)

• Physics - no question -

can't give an answer with no question. All you have done is present some data.

• Physics -

Oh, sorry I forgot to post the rest of the question.

(a) How far has she run after 64.7 s?

(b) What is the velocity of the runner at this point?

• Physics -

v= a •t,
t=v/a =5.7/1.35 = 4.2 s.
The distance covered for this time is
s1 = a •t²/2 = 1.35 •(4.22)²/2 =12 m.

If 64.7 is the total time of the motion, then the time
of uniform motion is
t1= 64.7 -4.2 =60.5 s.
The distance for this time is
s2 = v •t1 = 5.7 •60.5 =344.9 m.
The total distance is s1+s2 = 12 +344.9 = 356.9 m.

If 64.7 sec. is the time of uniform motion, then
s2 = 5.7 •64.7 =368.8 m.
Therefore, the total distance is
368.8 + 12 =380.8 m.
The velocity at this point is 5.7 m/s as she runs at a constant speed.

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