Which of the following pairs of forces are both non-contact forces?
Magnetic force and weight.
Weight and upthrust.
Air resistance force and electrostatic force.
Electrostatic force and friction force.
The figure shows two uncharged identical metal spheres A and B in contact and a positively charged metal rod, R, placed close to A but not touching it.
Without any further action, the charges on A and B are respectively.
Positive and positive.
Negative and positive.
Negative and uncharged.
Positive and negative.
If the distance between two charges Q₁, and Q₂ is doubled, the electrostatic force of repulsion between them will:
increase.
double.
reduce.
remain the same.
