Answer:
Little or no control is possible, relationships may be coincidental; cause-and effect relationships cannot be confirmed. Advantages of clinical method: Takes advantage of "natural clinical trials" and allows investigation of rare or unusual problems or events.
Explanation:
The time of motion of ball A before they collide is 5.1 seconds.
<h3>
Time of motion</h3>
The two balls will collide at a time "t" when they attain a certain height "h".
<h3>The equation of motion</h3>
The equation of motion of the two balls is given as follows;
<em />
<em>when they collide;</em>
- A would have traveled, (t + 4) seconds
- B would have traveled t seconds
![h_A = 30(t+ 4) - \frac{1}{2} g(t+ 4)^2\\\\h_B = 30t - \frac{1}{2} gt^2](https://tex.z-dn.net/?f=h_A%20%3D%2030%28t%2B%204%29%20-%20%5Cfrac%7B1%7D%7B2%7D%20g%28t%2B%204%29%5E2%5C%5C%5C%5Ch_B%20%3D%2030t%20-%20%5Cfrac%7B1%7D%7B2%7D%20gt%5E2)
![h_B = h_A\\\\30t - \frac{1}{2} gt^2 = 30(t + 4) - \frac{1}{2} g(t + 4)^2\\\\30t - \frac{1}{2} gt^2 = 30t + 120- \frac{1}{2}gt^2- 4gt -8g\\\\0 = 120 -4gt -8g\\\\4gt +8g = 120\\\\4(9.8)t + 8(9.8) = 120\\\\39.2t + 78.4 = 120\\\\39.2 t = 41.6\\\\t = \frac{41.6}{39.2} \\\\t = 1.1 \ s](https://tex.z-dn.net/?f=h_B%20%3D%20h_A%5C%5C%5C%5C30t%20-%20%5Cfrac%7B1%7D%7B2%7D%20gt%5E2%20%3D%2030%28t%20%2B%204%29%20-%20%5Cfrac%7B1%7D%7B2%7D%20g%28t%20%2B%204%29%5E2%5C%5C%5C%5C30t%20-%20%5Cfrac%7B1%7D%7B2%7D%20gt%5E2%20%3D%2030t%20%2B%20120-%20%5Cfrac%7B1%7D%7B2%7Dgt%5E2-%204gt%20-8g%5C%5C%5C%5C0%20%3D%20120%20-4gt%20-8g%5C%5C%5C%5C4gt%20%2B8g%20%3D%20120%5C%5C%5C%5C4%289.8%29t%20%2B%208%289.8%29%20%3D%20120%5C%5C%5C%5C39.2t%20%2B%2078.4%20%3D%20120%5C%5C%5C%5C39.2%20t%20%3D%2041.6%5C%5C%5C%5Ct%20%3D%20%5Cfrac%7B41.6%7D%7B39.2%7D%20%5C%5C%5C%5Ct%20%3D%201.1%20%5C%20s)
Thus, the time of motion of ball A before they collide is (1.1 + 4) = 5.1 seconds.
Learn more about time of motion here: brainly.com/question/2364404
Answer:
homogenity of the universe means that the universe is the same in all locations (there is no special location in the universe because in every location you look, the locations look the same) and this applies at larger scales.
isotropy of the universe means that the universe is the same in all directions (there is no special direction in the universe because its the same in every direction) this also applies in large scale.
no, the distribution of elephants on earth is not homogeneous and isotropic.
Explanation:
the distribution of elephants on earth exist in a small scale compared to the scales of the universe and on every location on earth you may choose, they are different numbers of elephants and in every direction on earth you look there are still different numbers of elephants.
here we know that volume of the drop is given as
![V = \frac{4}{3}\pi R^3](https://tex.z-dn.net/?f=V%20%3D%20%5Cfrac%7B4%7D%7B3%7D%5Cpi%20R%5E3)
![V = \frac{4}{3}\pi (1.35\times 10^{-3})^3](https://tex.z-dn.net/?f=V%20%3D%20%5Cfrac%7B4%7D%7B3%7D%5Cpi%20%281.35%5Ctimes%2010%5E%7B-3%7D%29%5E3)
![V = 1.03 \times 10^{-8} m^3](https://tex.z-dn.net/?f=V%20%3D%201.03%20%5Ctimes%2010%5E%7B-8%7D%20m%5E3)
now the mass of the drop is given as
![m = \rho V](https://tex.z-dn.net/?f=m%20%3D%20%5Crho%20V)
![m = 1.03 \times 10^{-5} kg](https://tex.z-dn.net/?f=m%20%3D%201.03%20%5Ctimes%2010%5E%7B-5%7D%20kg)
now the net buoyancy force on the drop is given as
![F_b = \rho_{air} V g](https://tex.z-dn.net/?f=F_b%20%3D%20%5Crho_%7Bair%7D%20V%20g)
![F_b = 1.2 (1.03\times 10^{-8})9.8](https://tex.z-dn.net/?f=F_b%20%3D%201.2%20%281.03%5Ctimes%2010%5E%7B-8%7D%299.8)
![F_b = 1.21\times 10^{-7} N](https://tex.z-dn.net/?f=F_b%20%3D%201.21%5Ctimes%2010%5E%7B-7%7D%20N)
now the net force on the drop is
![F = F_g - F_b](https://tex.z-dn.net/?f=F%20%3D%20F_g%20-%20F_b)
![F = 1.03\times 10^{-5}(9.8) - 1.21\times 10^{-7}](https://tex.z-dn.net/?f=F%20%3D%201.03%5Ctimes%2010%5E%7B-5%7D%289.8%29%20-%201.21%5Ctimes%2010%5E%7B-7%7D)
now acceleration of the drop is given as
![a = \frac{F}{m}](https://tex.z-dn.net/?f=a%20%3D%20%5Cfrac%7BF%7D%7Bm%7D)
![a = 9.79 m/s^2](https://tex.z-dn.net/?f=a%20%3D%209.79%20m%2Fs%5E2)
now the speed of the drop is given as
![v_f^2 - v_i^2 = 2 a d](https://tex.z-dn.net/?f=v_f%5E2%20-%20v_i%5E2%20%3D%202%20a%20d)
![v_f^2 - 0 = 2(9.79)(3950)](https://tex.z-dn.net/?f=v_f%5E2%20-%200%20%3D%202%289.79%29%283950%29)
![v_f = 278 m/s](https://tex.z-dn.net/?f=v_f%20%3D%20278%20m%2Fs)