Question

Dimas Pyrros (four-time Olympic medalist) raises a 215 kg barbell in two stages. In the
first stage he raises it to his shoulders, a height of 1.60 m, by exerting a maximum force of
3000 N. In the second stage he raises the barbell above his head at a constant speed to
a maximum height of 2.10 m. He then holds it above his head for 2.0 s before dropping it
to the mat.
(a) What is the magnitude of the force of gravity on the barbell?
(b) How much work did Pyrros do on the barbell to raise it to a height of 1.60 m?
(c) What is the magnitude of the force which the weightlifter must apply to raise the
barbell the last 0.60 m?
(d) How much work did the weightlifter do on the barbell to raise it the last 0.60 m?
(e) Draw a FBD of the barbell while it is held aloft for 2.0 s
(f) How much work did the weightlifter do on the barbell during those 2.0 s?

Answer 1

Hello,
I need to know the answer to the part (c) to (f).
thanks for the help

Answer 2

c, constant speed means force up = weight = m g in Newtons

d, weight in Newtons * 0.60 meters = work done in Joules

e, force up = weight down, no acceleration

f, force times distance = ZERO because no distance.