Answer:
Explanation:
Let the charge on bead A be q nC and the charge on bead B be 28nC - qnC
Force F between them
4.8\times10^{-4} = 
=120 x 10⁻⁸ = 9 x q(28 - q ) x 10⁻⁹
133.33 = 28q - q²
q²- 28q +133.33 = 0
It is a quadratic equation , which has two solution
q_A = 21.91 x 10⁻⁹C or q_B = 6.09 x 10⁻⁹ C
The only reasonable choice from this list is choice-A.
<span>The amount of heat energy needed to increase the temperature of a substance by </span>

<span> is given by:
</span>

<span>
where m is the mass of the substance, Cs is its specific heat capacity and </span>

<span> is the increase in temperature of the substance.
In this problem, we have a certain mass m of gold, with specific heat capacity </span>

<span>, to which we add Q=2825 J of energy. Its temperature increases by </span>

<span>. Therefore, if we re-arrange the previous equation, we can find the mass of the block of gold:
</span>

<span>
So, the correct answer is B.</span>