Answer:
Charge on least sphere, q = 570 nC
Step-by-step explanation:
It is given that,
Two small plastic spheres are given positive electrical charges. The distance between the spheres, r = 30 cm = 0.3 m
The repulsive force acting on the spheres, F = 0.13 N
If one sphere has four times the charge of the other.
Let charge on other sphere is, q₁ = q. So, the charge on first sphere is, q₂ = 4 q. The electrostatic force is given by :
![F=k(q_1q_2)/(r^2)](https://img.qammunity.org/2020/formulas/physics/high-school/uk8f4z91yssptetrk6ebnulp741i636gb7.png)
![0.13=9* 10^9* (q* 4q)/((0.3\ m)^2)](https://img.qammunity.org/2020/formulas/physics/college/x715r0t21j0qps2918ggt7tnl8g3xzjtu5.png)
![q^2=(0.13* (0.3)^2)/(9* 10^9* 4)](https://img.qammunity.org/2020/formulas/physics/college/xwfutby20aa5yrtk5jxnz0ju7gknnlinhb.png)
![q=5.7* 10^(-7)\ C](https://img.qammunity.org/2020/formulas/physics/college/pm8knoimh02f1p0bbkwgnyzd3tdb1fychv.png)
q = 570 nC
So, the charge on the least sphere is 570 nC. Hence, this is the required solution.