Subject: BiomechanicsAn 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?

Accepted Solution

Answer:   135.7 millisecondsStep-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 metersThe relationship between acceleration, velocity, and time is ...   v = atThe 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 sThe sprinter took about 135.7 ms to push off.