- #26

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You have two equations, one for the man and one for the dumbwaiter, and two unknowns, the acceleration and the tension.

So how do you find tension ?

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- #26

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You have two equations, one for the man and one for the dumbwaiter, and two unknowns, the acceleration and the tension.

So how do you find tension ?

- #27

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If not, see here

https://www.mathplanet.com/educatio...solving-systems-of-equations-in-two-variables

- #28

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The normal force between the man and the dumb waiter (we can ignore the scale since that is considered massless, so just transmits the force straight through) must be up on one and down on the other. Does it act down on the man and up on the dumb waiter or the other way around?It’s going up , so shouldn’t it be added to tension

- #29

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The normal force between the man and the dumb waiter (we can ignore the scale since that is considered massless, so just transmits the force straight through) must be up on one and down on the other. Does it act down on the man and up on the dumb waiter or the other way around?

Wouldn’t it be the other way around ? Up on the man and down on the dumbwaiter ?

- #30

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- #31

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My teacher explained to use two different equations when two variables are unknown, I was trying to find another equation to substitute T with

- #32

SammyS

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You have the correct information for the man in post #5.My teacher explained to use two different equations when two variables are unknown, I was trying to find another equation to substitute T with

Use 209 newtons for FFn=209N (the scale reading)

Fg=mg

=(82kg)(9.8) = 803.6 N

And the force exerted on the rope is T

So the formula would be,

(Fn +T)-Fg=ma

Am I wrong or missing something ?

Then as @kuruman wrote, your equation in post #22 is correct.

Use those two equations to eliminate T (or eliminate a if you'd rather find the tension).Oh, I see

So then it’ll be

T-209N-40g=40a ?

- #33

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Right, but in post #16 you had an equation for the dumb waiter with T....+Fn = ...Wouldn’t it be the other way around ? Up on the man and down on the dumbwaiter ?

If the tension is acting upwards on the dumb waiter and the normal force is acting downwards then they cannot both be positive on the same side of tne equation.

- #34

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I have a suggestion for OP, @y90x. Why don't you write two equations for Newton's 2nd Law, F_{net} = ma, one for which the system is the man and one for which the system is the dumbwaiter and in which **only symbols** appear, not numbers, and post them. One (or more) of us will review these equations and point out what is wrong (if anything) with them. At this point, it seems to me there is some tail-chasing going on here so a fresh start would be beneficial.

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