Answer:
Time taken, 
Explanation:
It is given that, a small metal ball is suspended from the ceiling by a thread of negligible mass. The ball is then set in motion in a horizontal circle so that the thread’s trajectory describes a cone as shown in attached figure.
From the figure,
The sum of forces in y direction is :
Sum of forces in x direction,
.............(1)
Also, 
Equation (1) becomes :
...............(2)
Let t is the time taken for the ball to rotate once around the axis. It is given by :
Put the value of T from equation (2) to the above expression:
On solving above equation :
Hence, this is the required solution.
When the car speeds up, slows down, or goes around a curve,
passengers need a force applied to them to make them do the
same thing, otherwise they won't keep up with the car.
The force on the passenger is applied by means of friction between
the upholstery and the seat of his pants, and also by the seat-back
or his seat-belt.
The correct answer is A. Acid rain forms from human activities and lowers the pH of rainwater below 7
Explanation:
The term "acid rain" is used to refer to rainwater with a low pH or a high acidity, this includes rainwater with a pH below 7 (solutions with a pH under 7 are acidic). In terms of formation, acid rain is mainly the result of human activities such as factories or cars that release pollutants into the atmosphere including nitric and sulfuric acids and these alter the natural pH of rain and makes it more acidic. Additionally, acid rain has negative consequences such as the death of fishes and other organisms in lakes, rivers, etc. because the acidity is toxic to many organisms. Thus, acid rain is the result of human activities and it lowers the pH of rain (Option A).
