A laboratory experiment was done to show the effects of organic waste on the dissolved oxygen (DO) content in water. Five tanks were set up, each containing fresh water and a small amount of single-celled green algae. Specified amounts of organic waste were added to the tanks. The results below show the amount of DO in each tank after a period of one week.
Tank 1 Tank 2 Tank 3 Tank 4 Tank 5
Initial DO 10 ppm 10 ppm 10 ppm 10 ppm 10 ppm Amount of organic Waste added
0 g 10 g 20 g 30 g 40 g
DO after one week
10 ppm 10 ppm 8 ppm 5 ppm 0 ppm
Which of the following would best improve the validity of the experiment?
a. Increasing the amounts of green algae in each of the tanks, with tank 5 having the greatest amount
b. Eliminating tank 1, because the DO stayed the same.
c. Adding different types of waste to each tank and then checking the results.
d. Repeating the experiment several times and comparing the results.

A23 kg log of wood begins from rest, 300 m up a sluice (a water track used to transport logs, think of it as an inclined plane with negligible friction) inclined at 20° to the horizontal. after it reaches the flat waterway at the bottom it collides elastically with a 100 kg block of wood initially at rest near the base of the incline. (a) how long does it take the 23 kg log to travel down the incline? (b) what is the speed of the 23 kg log at the bottom of the incline? (c) what are the velocities of both blocks of wood after the collision? (d) what is the total kinetic energy before the collision? (e) what is the kinetic energy of the 23 kg log after the collision? (f) what is the kinetic energy of the 100 kg block of wood after the collision? (g) what is the total kinetic energy after the collision? (h) compare the total initial and total final kinetic energies. is this consistent with what you would expect for elastic collisions? explain!

If element x has 99 protons how many electrons does it have

The field between two charged parallel plates is kept constant. if the two plates are brought closer together, the potential difference between the two plates either a) decrease b) does not change c) increase?