Help with two Physics problems?

Test Preparation SAT Subject Test Preparation
1

<p>An explanation would be greatly appreciated! I'm so lost. :(</p>

<ol>
<li><p>Three charges are on the y-axis. One positive charge, q1 = 9.0 x 10^-6 C, is at y = 3.0 m. A second charge of -19 x 10^-6 C is located at the origin. A third charge of 9.0 x 10^-6 C is placed so that q2 is in electrostatic equilibrium with q1 and q2. How large must the electrostatic force between q2 and q3 be to balance the force between q1 and q2?</p></li>
<li><p>Three charges lie along the x-axis. One positive charge, q1 = 25 x 10^-6 is at x = 0.25 m. Another charge, q2 = -5.0 x 10^-6 C, is located at the origin. A third charge, q3 = 35 x 10^-6 C, is placed so that q2 is in the electrostatic equilibrium of q1 and q3. How large must the electrostatic force between q2 and q3 be to balance the force between q1 and q2?</p></li>
</ol>

<p>Any help would be great! I fail at physics.</p>

2

<p>bummmpppp!!</p>

3

<p>the force between q1-q2 and the force between q2-q3 are equal because q1 and q3 have the same charge but the forces are in opposite directions. </p>

<p>Use the equation k<em>q1</em>q2/(r^2)</p>

<p>Since charge of q1 and q3 are the same, for q2 to be in equilibrium, the distance of q1 to q2 and q2 to q3 have to be equal. Therefore, substitute 3 for r.</p>

<p>k<em>q1</em>q2/9</p>

<p>k is couloumb’s constant</p>

4

<p>thanks! :)</p>