An athlete whose mass is 85.5 kg is performing weight-lifting exercises. Startin

Question

An athlete whose mass is 85.5 kg is performing weight-lifting exercises. Starting from the rest position, he lifts, with constant acceleration, a barbell that weights 460 N. He lifts the barball a distance of 0.50 m in a time of 1.6 s.

1.) Use Newtons laws to find the total force that his feet exert on the groud as he lifts the barbell.

Ffloor =  ? N

I have no idea how to figure this problem out. Everything I've been doing is wrong. Please show step by step with correct answers so I can try to understand.

THANK YOU!

Explanation / Answer

Total force (Ffloor) = Weight of athlete + Barbell

Weight of athlete = (85.5 kg)(9.81 m/s^2) = 838.755 N

Barbell is being lifted upwards, so its weight on the athlete's foot ends up being mass*(gravity +acceleration of lift).

Mass of barbell = 460 N / 9.81 m/s^2 = 46.891 kg

Using the kinematic equation d = (Vi)(t) + (1/2)(a)(t^2), we can solve for acceleration and get a = 0.3906 m/s^2

Add that acceleration to gravity, then multiply by the mass and you get (9.81 + 0.3906 m/s^2)(46.891 kg) = 478.3 N

So, Ffloor = 838.755 N + 478.3 N = 1317.06 N of force exerted by his feet

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