Four equal masses m are fixed at the vertices of a square of side a. A particle of mass m₀ is brought quasistatically from infinity to the centre. Work done by the external agent is:
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Four equal masses m are fixed at the vertices of a square of side a. A particle of mass m₀ is brought quasistatically from infinity to the centre. Work done by the external agent is:

G1 Physics · Accepted Answer

Distance of each vertex from centre is a/√2. Potential at centre V=4[−Gm/(a/√2)]=−4√2Gm/a. Quasistatic external work equals ΔU=m₀V=−4√2Gmm₀/a.