Answer:
2.12 × 10⁻⁷ C
Step-by-step explanation:
Given:
Charge on the glass sphere, Q = 10.9 nC = 10.9 × 10⁻⁹ C
Distance between the glass and the metal sphere, r = 4.0 cm = 0.04 m
Force experienced by the metal sphere, F = 0.0130 N
let the charge on the metal sphere be 'q'
Now,
the force due to a charge on the other charge is given as:

where,
k is the coulomb's constant = 9 × 10⁹ N.m²/C²
on substituting the values in the formula, we get

or
q = 2.12 × 10⁻⁷ C