Example of surface events are erosion and weathering. Erosion is the carrying of a particle from one place to the other and weathering is the breaking down of particles. These processes help in rock formation because this allows physical changes (grouping together or breaking down) on a certain substance. Subsurface events are those which happened underground such as the flow of underground water which subsequently allow the deposition of minerals, etc.
Frictional force and Applied force has same “magnitude” and “opposite” direction.
Option: B
<u>Explanation</u>:
When a book is moved horizontally by applying “force” on the book, the frictional force is opposed to the book by the table. Here, this “frictional force” is opposing the book has the same force what we applied on the book but this frictional force and the applied force are opposite in direction. Always the “frictional force” is opposite to the “applied force” which stops the object to move. For example, if a force applied leftward to the object the frictional force is acted on the right side of the object.
When two objects are in contact they experience a "frictional force". This "frictional force" acts opposite to the force applied on to move the object.
Formula for "frictional force" is 
Where,
is coefficient of friction and N is normal force.
The earth is 4.54 billion years old.
The guy that answered this is fake and he’s doing it for free points so
Just repost it and hope he doesn’t find it
Explanation:
It is given that, the range of human hearing is roughly from twenty hertz to twenty kilohertz.
Minimum frequency, f = 20 Hz
Maximum frequency, f' = 20,000 Hz
We need to find the lengths of the longest and shortest pipes. For open pipes, the length of pipe is given by :

For shortest pipe, frequency should be maximum, 
l = 0.008575 m
For longest pipe, frequency should be minimum, 
l' = 8.575 m
So, the lengths of longest and shortest pipes are 8.575 meters and 0.008575 meters respectively.