An athlete whose mass is 85.5 kg is performing weight-lifting exercises. Startin
ID: 2273772 • Letter: A
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