The runner (mass = 60 kg) is running in the positive horizontal (X) direction (F

Question

The runner (mass = 60 kg) is running in the positive horizontal (X) direction (Fig. 1). The runner's horizontal acceleration is 14 m/s^2 and is in the same direction he is running. Additionally, the magnitude of the horizontal and vertical ground reaction forces (GRF^rightarrow _x v) are 800 N and 980 N, respectively. Answer the following. For each part of the question, clearly indicate the equation you are using. A. What is the runner's vertical acceleration? B. What are the magnitude and direction theta (relative to the horizon) of the resultant ground reaction force (RF^rightarrow) acting on the foot?

Explanation / Answer

3. In horizontal,

a_x = Fx / m

m = 800 / 14 = 57.14 kg ....this is the mass of runner.

In vertical,

ay = Fy / m = 980 / 57.14

ay = 17.15 m/s^2 ........Ans

(B) RF = sqrt(Fx^2 + Fy^2)

= 1265 N

direction, theta = tan^-1(Fy/Fx)

= 50.8 deg

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