# 8 questions (Essentials of physics)

8 questions of physics

1

Use (10.1.1) with r = 0.01m. We’re told that q1 = q2, so you can replace q2 by q1 and then solve for q1.

2

Again use (10.1.1). You don’t need to know the result of the last problem. We know what the force at r = 0.01m is: F = 0.001N. Now we want to increase the distance to rnew = 0.05m. To find out how this changes the force, form the ratio between the unknown new force and the previous force:

Fnew =? F

The charges q1 and q2 in the formula for Fnew and F are unchanged, so q1 and q2 cancel in the ratio on the right-hand side. Only the ratio between r and rnew will appear – and you know its value. You should get a force that’s a lot smaller than F from problem 1.

3

Again use (10.1.1). The mass in kg isn’t relevant to the answer.

4

Again use (10.1.1), making sure to use meters and not km for the distance r. Also state if the force is force is attractive or repulsive.

5

Again use (10.1.1): solve for r. 7

Use (10.2.1)

10

Again use (10.2.1): solve for the field by dividing both sides by the charge (also specify the direction of the field).

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