Question Number 203726 by mr W last updated on 27/Jan/24

Commented by mr W last updated on 26/Jan/24

Answered by mr W last updated on 27/Jan/24

Commented by mr W last updated on 26/Jan/24

Commented by mr W last updated on 27/Jan/24

Commented by mr W last updated on 26/Jan/24

Commented by mr W last updated on 27/Jan/24

Commented by mr W last updated on 27/Jan/24
![the center of mass of the three charges is G, which in current case must be the centroid of ΔABC, since they have the same mass. G must lie vertically under the hanging point S on the ceiling. say the sides of ΔABC are p, q, r respectively. m_A =AP=((√(2(q^2 +r^2 )−p^2 ))/2) m_B =BQ=((√(2(r^2 +p^2 )−q^2 ))/2) m_C =CR=((√(2(p^2 +q^2 )−r^2 ))/2) d_A =(2/3)m_A =distance from G to A d_B =(2/3)m_B =distance from G to B d_C =(2/3)m_C =distance from G to C say SG=h, SG is vertical. F_1 =((kQ^2 )/p^2 ) with Q=charge, k=Coulomb constant F_2 =((kQ^2 )/q^2 ) F_3 =((kQ^2 )/r^2 ) say F_A is the resultant from F_2 and F_3 F_B is the resultant from F_3 and F_1 F_C is the resultant from F_1 and F_2 T_A , F_A and mg must be in the same plane and in equilibrium. (F_A /d_A )=(T_A /a)=((mg)/h) ⇒F_A =((mgd_A )/h), T_A =((mga)/h) similarly F_B =((mgd_B )/h), T_B =((mgb)/h) F_C =((mgd_C )/h), T_C =((mgc)/h) (F_2 /(0.5q))=(F_3 /(0.5r))=(F_A /m_A )=((mgd_A )/(hm_A ))=((2mg)/(3h)) F_2 =((mgq)/(3h))=((kQ^2 )/q^2 ) ⇒q=(((3kQ^2 h)/(mg)))^(1/3) F_3 =((mgr)/h)=((kQ^2 )/r^2 ) ⇒r=(((3kQ^2 h)/(mg)))^(1/3) similarly F_1 =((mgp)/h)=((kQ^2 )/p^2 ) ⇒p=(((3kQ^2 h)/(mg)))^(1/3) that means p=q=r=(((3kQ^2 h)/(mg)))^(1/3) =((3μ^2 h))^(1/3) with μ=(√((kQ^2 )/(mg))) SP=h_P =((√(2(b^2 +c^2 )−p^2 ))/2) m_A (h^2 +(1/3)m_A ×(2/3)m_A )=(m_A /3)×a^2 +((2m_A )/3)×h_P ^2 h^2 +(2/9)m_A ^2 =(a^2 /3)+((2h_P ^2 )/3) h^2 +(2/9)×((2(q^2 +r^2 )−p^2 )/4)=(a^2 /3)+((2(b^2 +c^2 )−p^2 )/6) h^2 +((p^2 +q^2 +r^2 )/9)=((a^2 +b^2 +c^2 )/3) 9h^2 +p^2 +q^2 +r^2 =3(a^2 +b^2 +c^2 ) 9h^2 +3((9μ^4 h^2 ))^(1/3) −3(a^2 +b^2 +c^2 )=0 let δ=(√(a^2 +b^2 +c^2 )) ((h^2 )^(1/3) )^3 +(1/3)((9μ^4 ))^(1/3) ((h^2 )^(1/3) )−(δ^2 /3)=0 ⇒(h^2 )^(1/3) =(((1/3)(√((δ^4 /4)+(μ^4 /9)))+(δ^2 /6)))^(1/3) −(((1/3)(√((δ^4 /4)+(μ^4 /9)))−(δ^2 /6)))^(1/3) ⇒h=[(((1/3)(√((δ^4 /4)+(μ^4 /9)))+(δ^2 /6)))^(1/3) −(((1/3)(√((δ^4 /4)+(μ^4 /9)))−(δ^2 /6)))^(1/3) ]^(3/2) (T_A /(mg))=(a/h)=(a/([(((1/3)(√((δ^4 /4)+(μ^4 /9)))+(δ^2 /6)))^(1/3) −(((1/3)(√((δ^4 /4)+(μ^4 /9)))−(δ^2 /6)))^(1/3) ]^(3/2) )) (T_B /(mg))=(b/h)=(b/([(((1/3)(√((δ^4 /4)+(μ^4 /9)))+(δ^2 /6)))^(1/3) −(((1/3)(√((δ^4 /4)+(μ^4 /9)))−(δ^2 /6)))^(1/3) ]^(3/2) )) (T_C /(mg))=(c/h)=(c/([(((1/3)(√((δ^4 /4)+(μ^4 /9)))+(δ^2 /6)))^(1/3) −(((1/3)(√((δ^4 /4)+(μ^4 /9)))−(δ^2 /6)))^(1/3) ]^(3/2) )) special case: a=b=c=s T_A =T_B =T_C =T (T/(mg))=(s/([(((√((s^4 /4)+(μ^4 /(81))))+(s^2 /2)))^(1/3) −(((√((s^4 /4)+(μ^4 /(81))))−(s^2 /2)))^(1/3) ]^(3/2) ))](https://www.tinkutara.com/question/Q203733.png)
Commented by ajfour last updated on 26/Jan/24

Commented by mr W last updated on 26/Jan/24

Commented by mr W last updated on 27/Jan/24

Commented by ajfour last updated on 27/Jan/24
At least i understood now that p=q=r, very remarkable!
Answered by mr W last updated on 27/Jan/24

Commented by mr W last updated on 27/Jan/24

Commented by mr W last updated on 27/Jan/24

Commented by mr W last updated on 27/Jan/24

Commented by mr W last updated on 28/Jan/24

Commented by mr W last updated on 28/Jan/24

Commented by mr W last updated on 27/Jan/24

Commented by mr W last updated on 28/Jan/24
![say the center of mass of the three charges is G, which must lie vertically under the hanging point S on the ceiling. say the sides of ΔABC are p, q, r respectively. (p_1 /p)=(M_C /(M_B +M_C )) ⇒p_1 =((M_C p)/(M_B +M_C )) (p_2 /p)=(M_B /(M_B +M_C )) ⇒p_2 =((M_B p)/(M_B +M_C )) m_A =AP p(m_A ^2 +p_1 p_2 )=p_1 q^2 +p_2 r^2 m_A ^2 +((M_B M_C p^2 )/((M_B +M_C )^2 ))=((M_C q^2 +M_B r^2 )/(M_B +M_C )) ⇒m_A ^2 =((M_C q^2 +M_B r^2 )/(M_B +M_C ))−((M_B M_C p^2 )/((M_B +M_C )^2 )) (d_A /m_A )=((M_B +M_C )/(M_A +M_B +M_C )) (e_A /m_A )=(M_A /(M_A +M_B +M_C )) say SG=h, SG is vertical. F_1 =((kQ_B Q_C )/p^2 ) with k=Coulomb constant F_2 =((kQ_C Q_A )/q^2 ) F_3 =((kQ_A Q_B )/r^2 ) say F_A is the resultant from F_2 and F_3 F_B is the resultant from F_3 and F_1 F_C is the resultant from F_1 and F_2 T_A , F_A and M_A g must be in the same plane and in equilibrium. (F_A /d_A )=(T_A /a)=((M_A g)/h) ⇒F_A =((M_A gd_A )/h), T_A =((M_A ga)/h) similarly F_B =((M_B gd_B )/h), T_B =((M_B gb)/h) F_C =((M_C gd_C )/h), T_C =((M_C gc)/h) (F_2 /((p_1 /p)×q))=(F_3 /((p_2 /p)×r))=(F_A /m_A )=((M_A gd_A )/(hm_A ))=((M_A (M_B +M_C )g)/((M_A +M_B +M_C )h)) ⇒F_2 =((M_C M_A gq)/((M_A +M_B +M_C )h))=((kQ_C Q_A )/q^2 ) ⇒q^3 =((kQ_C Q_A (M_A +M_B +M_C )h)/(gM_C M_A )) ⇒F_3 =((M_A M_B gr)/((M_A +M_B +M_C )h))=((kQ_A Q_B )/r^2 ) ⇒r^3 =((kQ_A Q_B (M_A +M_B +M_C )h)/(gM_A M_B )) similarly ⇒p^3 =((kQ_B Q_C (M_A +M_B +M_C )h)/(gM_B M_C )) let μ_1 =(√((kQ_B Q_C (M_A +M_B +M_C ))/(gM_B M_C ))) μ_2 =(√((kQ_C Q_A (M_A +M_B +M_C ))/(gM_C M_A ))) μ_3 =(√((kQ_A Q_B (M_A +M_B +M_C ))/(gM_A M_B ))) ⇒p=((μ_1 ^2 h))^(1/3) , q=((μ_2 ^2 h))^(1/3) , r=((μ_3 ^2 h))^(1/3) SP=h_P p(h_P ^2 +p_1 p_2 )=p_1 c^2 +p_2 b^2 h_P ^2 +((M_B M_C p^2 )/((M_B +M_C )^2 ))=((M_C c^2 +M_B b^2 )/(M_B +M_C )) h_P ^2 =((M_B b^2 +M_C c^2 )/(M_B +M_C ))−((M_B M_C p^2 )/((M_B +M_C )^2 )) m_A (h^2 +e_A d_A )=e_A a^2 +d_A ×h_P ^2 h^2 +e_A d_A =((M_A a^2 )/(M_A +M_B +M_C ))+(((M_B +M_C )h_P ^2 )/(M_A +M_B +M_C )) h^2 +((M_A (M_B +M_C )m_A ^2 )/((M_A +M_B +M_C )^2 ))=((M_A a^2 )/(M_A +M_B +M_C ))+(((M_B +M_C )h_P ^2 )/(M_A +M_B +M_C )) h^2 +((M_A (M_B +M_C ))/((M_A +M_B +M_C )^2 ))×[((M_C q^2 +M_B r^2 )/(M_B +M_C ))−((M_B M_C p^2 )/((M_B +M_C )^2 ))]=((M_A a^2 )/(M_A +M_B +M_C ))+(((M_B +M_C ))/(M_A +M_B +M_C ))×[((M_B b^2 +M_C c^2 )/(M_B +M_C ))−((M_B M_C p^2 )/((M_B +M_C )^2 ))] h^2 +((M_B M_C p^2 +M_C M_A q^2 +M_A M_B r^2 )/((M_A +M_B +M_C )^2 ))=((M_A a^2 +M_B b^2 +M_C c^2 )/(M_A +M_B +M_C )) h^2 +(((M_B M_C (μ_1 ^4 )^(1/3) +M_C M_A (μ_2 ^4 )^(1/3) +M_A M_B (μ_3 ^4 )^(1/3) )(h^2 )^(1/3) )/((M_A +M_B +M_C )^2 ))−((M_A a^2 +M_B b^2 +M_C c^2 )/(M_A +M_B +M_C ))=0 let ξ=((M_B M_C (μ_1 ^4 )^(1/3) +M_C M_A (μ_2 ^4 )^(1/3) +M_A M_B (μ_3 ^4 )^(1/3) )/((M_A +M_B +M_C )^2 )) or ξ=((((M_A M_B M_C )/((M_A +M_B +M_C )^4 ))×(((kQ_A Q_B Q_C )/g))^2 ))^(1/3) [(1/( ((M_A Q_A ^2 ))^(1/3) ))+(1/( ((M_B Q_B ^2 ))^(1/3) ))+(1/( ((M_C Q_C ^2 ))^(1/3) ))] δ=((M_A a^2 +M_B b^2 +M_C c^2 )/(M_A +M_B +M_C )) ((h^2 )^(1/3) )^3 +ξ((h^2 )^(1/3) )−δ=0 ⇒(h^2 )^(1/3) =(((√((δ^2 /4)+(ξ^3 /(27))))+(δ/2)))^(1/3) −(((√((δ^2 /4)+(ξ^3 /(27))))−(δ/2)))^(1/3) ⇒h=[(((√((δ^2 /4)+(ξ^3 /(27))))+(δ/2)))^(1/3) −(((√((δ^2 /4)+(ξ^3 /(27))))−(δ/2)))^(1/3) ]^(3/2) (T_A /(M_A g))=(a/h) (T_B /(M_B g))=(b/h) (T_C /(M_C g))=(c/h)](https://www.tinkutara.com/question/Q203766.png)
Commented by ajfour last updated on 28/Jan/24
