100 kg elevator acclerates up at rate avg a*. What's the avg force acting on the elevator if it covers a distance X over a period of 10s?(adsbygoogle = window.adsbygoogle || []).push({});

a* denotes average accleration

a. 2X + 1000

b. 100(a* + 1)

c. 2a* + 1000

d. 2a*X

I set up a free body diagram to show all the forces acting on the elevator. There's a downward force due to gravity, Fg, the net upward force, Fn, causing the accleration.

Fn - Fg = ma*

Fn = ma* + Fg

The question states that it travels a distance of X over 10 sec

a* = delta V/delta t

delta V = X/t , which the question gives me

delta V = x/10s, i substituted this into the a* equation and got

a* = x/100s

when i plug this into my net force equation:

Fn = ma* + Fg

Fn = m(a* + g)

Fn = 100kg(x/100s + 10m/s^2)

Fn = X + 1000

I can't seem to figure out why my answer doesn't match any of the answer choices. Can someone please point out what i'm doing wrong?

Thanks

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# Homework Help: Elevator question

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