- #1

arhzz

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- Homework Statement
- A man tries to convince his wife with a trick that he has already lost a lot. He stands on a scale in an elevator. His mass is 95 kg. As soon as the elevator starts going down, he shows his wife the display.

a) The elevator accelerates at 0.2 g when leaving the floor. The scale is showing a mass of (blank) at this moment.That corresponds to a force of (blank)

b)Bad luck, but the wife also looks at the display when the elevator descends at a constant speed of 2.0 m / s. She sees a mass of (blank)

- Relevant Equations
- F = m*g

Hello! Now what I've done is first calculate the acceleration. a = 1,962 m/s^2. Than I tried looking at the solution simply through the Newtons laws (or axioms I don't know how to say it in english). Since the elevator is moving through the air the gravitation constant has to be taken into account.Than I've used this property; $$

\frac{m1}{m2} = \frac{a2}{a1}$$ Now I have one mass and one accelartion(the one I calculated) we are looking for m2 so we only need a2,I took a2 to be g since the way I see it we have 2 Forces,one where the elevator accelerates and the second the one where the elevator is getting pulled down by F = m*g. So after that I did this. $$ m2 = \frac{m1a1}{a2} kg$$ m2 comes out to be 19kg.Now this doesn't really seem realistic to me.I've looked at some other formulas and I've stumbled upon this one $$ a = \frac{m2}{m1+m2} * g $$ Now this should apply to my problem,I just don't know how to get an expression for m2,the algebra doesn't add up.My intuition tells me that somehow I should get to a form where m2 = m1 -19 = 76kg,and than we can easily calcualte the Force (with 76kg should be 745,56N).

Any insights?for b) I haven't tried anything yet,kind of stuck on a.Thank you!

\frac{m1}{m2} = \frac{a2}{a1}$$ Now I have one mass and one accelartion(the one I calculated) we are looking for m2 so we only need a2,I took a2 to be g since the way I see it we have 2 Forces,one where the elevator accelerates and the second the one where the elevator is getting pulled down by F = m*g. So after that I did this. $$ m2 = \frac{m1a1}{a2} kg$$ m2 comes out to be 19kg.Now this doesn't really seem realistic to me.I've looked at some other formulas and I've stumbled upon this one $$ a = \frac{m2}{m1+m2} * g $$ Now this should apply to my problem,I just don't know how to get an expression for m2,the algebra doesn't add up.My intuition tells me that somehow I should get to a form where m2 = m1 -19 = 76kg,and than we can easily calcualte the Force (with 76kg should be 745,56N).

Any insights?for b) I haven't tried anything yet,kind of stuck on a.Thank you!

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