Answer:
A) some of the rocks energy is transformed to thermal energy
Explanation:
If we neglect air resistance during the fall of the rock, than the mechanical energy of the rock (which is sum of its potential energy and its kinetic energy) would be constant during the entire motion, so the total energy of the rock at the top would be the same as the sum of its potential energy and kinetic energy at the bottom.
However, this not occurs, due to the presence of air resistance. In fact, air resistance acts against the fall of the rock, and because of the friction between the molecules of air and the surface of the rock, the rock loses part of its energy. This energy is converted into thermal energy of the molecules of the air.
Because it stretches and makes your muscles ready for the activity
Answer:
see below
Explanation:
First, the obvious, as you press the gas pedal harder the acceleration goes up as well. Conversely, is you do not press the pedal, you will not accelerate. This determines that is I press the gas pedal, it will CAUSE the car to accelerate. This proves causation.
Now, correlation. The definition of correlation in statistics is any statistical relationship between two random variables or data. This simply means that these two events are connected to one another. A POSITIVE correlation is when two correlated events move in the same direction as one another. I have added a graph to help visualize this. In this problem as the gas is pressed harder, the acceleration increases. If the pressure on the pedal was decreased, then the acceleration also decreases. If the pressure on the pedal is constant, the the acceleration is constant.
I hope this helps!
By looking at the acceleration of the object.
In fact, Netwon's second law states that the resultant of the forces acting on an object is equal to the product between the mass m of the object and its acceleration:

So, when static friction is acting on the object, if the object is still not moving we know that all the forces are balanced: in fact, since the object is stationary, its acceleration is zero, and so the resultant of the forces (left term in the formula) must be zero as well (i.e. the forces are balanced).