. Point charges q1 = q2 = 4.0 × 10−6 C are fixed on the x-axis at x = −3.0 m and x = 3.0 m. What charge q must be placed at the origin so that the electric field vanishes at x = 0, y = 3.0 m?

Explanation:

Electric Field

The total electric field is the sum of all the individual electric fields produced by each charge. Please refer to the image below. The charges q1 and q2 produce the electric fields shown in the point (0,3). Since both charges are equal in magnitude and sign and are at the same distance from the point, the horizontal component of their electric fields cancel each other, only the vertical component remains and it's directed upwards.

The third charge q3 must be negative, so the total electric field is zero. Let's first compute the value of the angle by analyzing the distances in the right triangle formed by the charges q1, q2, and the point (0,3)

It follows that

The distance from q1 (or q2) to the point (0,3) is computed by

Let's compute the magnitude of the electric of q1 or q2:

The vertical component of both fields is given by

The total field produced by q1 and q2 is twice that quantity

That should be the value of E3 to make the total field vanish (equal to 0)

Solving for q3

We had already established the sign of q3 must be negative

c. newton's third law of motion

when jerome paddle in flowing river towards east the net speed of jerome will increase

so the net speed of jerome will be given as

now the speed of paul will be same as it is given as he is running on the ground

so

so here we can say since the speed of jerome is more so he will win the race

now as we know the distance so the time difference is given as

so jerome will reach first and the time difference will be 203.55 s or 3.4 min