A10 kg block is pushed with a constant horizontal force of 20 n against a constant horizontal frictional force of 10 n. what is the acceleration of the block?

The acceleration would be a=1 m/s^2. Let's explain why.

Explanation:

Let's say the block is □

20N→□    Block is pushed with a constant horizontal force of 20N

□←10N     It is known that frictional force is the opposite way of the movement

So it is safe to say that there is 10 N force trying to stop the block.

In this case our net force is

According to Newton's second motion law

(m=mass, F=force, a=acceleration

→

As an extra information the block also applies gravitational m.g force down but since there is no other force applies in the vertical way, ground compansate the force.

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.