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EK ICE1 Question 5
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leahjinx
#1 Posted : Friday, June 15, 2018 6:07:56 PM
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Hey,

I'm completely lost on this question. I understand that the muscle force will be reduced as the force required to life the weight is less because the Fg in the opposite direction is decreased. I don't understand how the decreased Fg doesn't change acceleration?

I'm not sure if this makes sense but is it because if the upward force (muscle force) is decreased and the downward force (Fg) is decrease then the overall Fnet stays the same, so ma would also be the same?
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mhamw
#2 Posted : Saturday, June 16, 2018 2:45:41 PM
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Hi leahjinx,

You are on the right track. You can break up this problem into 2 parts.

Part 1: isometric contraction --> F(net) = 0
F(gravity) is reduced, so F(muscle) is reduced.
You can think of this part as "controlling for gravity".

Part 2: concentric contraction --> F(net) > 0
The added F(muscle) is the same, so F(net) is the same.
Thus, acceleration will also be the same.

Although a smaller F(muscle) is used to control for gravity, the isometric contraction in both cases brings the system to equilibrium before increasing the stimulation by an equal amount.

Regards,
Milad
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