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Subject: Biomechanics

An 85 kg sprinter pushes off from the blocks and experiences an average resultant reaction force of 2000 N at an angle of 20 degrees to the horizontal. If the sprinter left the blocks with a horizontal velocity of 3 m/s, how long was sprinter in contact with the blocks?

Answer :

sqdancefan

Answer:

  135.7 milliseconds

Step-by-step explanation:

The relationship between force, mass, and acceleration is ...

  F = Ma . . . . . we use M for mass, so as not to confuse with m for meters

The relationship between acceleration, velocity, and time is ...

  v = at

The fraction of the applied force that is in the horizontal direction is ...

  2000N·cos(20°)

Solving for a and t, we get ...

  a = F/M

  t = v/a = v/(F/M) = Mv/F

  t = (85 kg)(3 m/s)/(2000cos(20°) kg·m/s²) ≈ 0.1357 s

The sprinter took about 135.7 ms to push off.

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