If a ball takes 12 seconds to hit the ground, how fast was it falling when it hit the ground?

Roughly around 117.6 mph

Explanation

To find out something's speed (or velocity) after a certain amount of time, you just multiply the acceleration of gravity by the amount of time since it was let go of. So you get: velocity = -9.81 m/s^2 * time, or V = gt. The negative sign just means that the object is moving downwards.

you would expect a sound wave to speed up. - b)

electric field is a function of 1/r^2

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