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i am trying to calculate simple problem from physic,but i am getting somehow wrong answer.problem is that what is a mass of bag which is hold by child with mass $50$KG,if there is force of heaviness on both which is equal $600$N

so in shortly,we know that on child and bag,there works $600$N force of heaviness,we have to find mass of bag. as i know force of heaviness on mass on earth is $F=m*g$ if we have two mass,then i think formula would be $F=m_1*m_2*g$ from which $m_2=1.2$,but in book answer is $m_2=10kg$,please help me to clarify why is so?

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Shouldn't the formula be $F=(m_1+m_2)g$? –  draks ... Jul 19 '12 at 8:36
    
aa right yes,i have mixed something,thanks very much –  dato datuashvili Jul 19 '12 at 8:40
    
maybe $F=G\frac{m_1m_2}{r^2}$? is this homework? or are you doin' this for fun or research? –  draks ... Jul 19 '12 at 8:41
    
no for myself working –  dato datuashvili Jul 19 '12 at 8:48
    
thanks for downvoter –  dato datuashvili Jul 27 '12 at 14:01
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3 Answers 3

up vote 1 down vote accepted

Your formula is wrong. Take $F=(m_1+m_2)g=(50kg+10kg)9.81\frac{m}{s^2}\approx 600N$.

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It should be $(m_1+m_2)g$, where m1+m2 is the total mass, why are you multiplying? But I don't think this is the right place for such a question. I believe physics tag was not meant for this.

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The mass of child plus bag is $M = m_1+m_2$. So the force for this sum is $F=M\cdot g = 600$N with $g \approx 10 \frac{m}{s^2}$. Since $m_2$ (the mass of the child) is $50$kg:

$$ m_1 = \frac{F}{g}-m_2 = 10 \text{kg} $$

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