Because there's no such thing as "really" moving.
ALL motion is always relative to something.
Here's an example:
You're sitting in a comfy cushy seat, reading a book and listening
to your .mp3 player, and you're getting drowsy. It's so warm and
comfortable, your eyes are getting so heavy, finally the book slips
out of your hand, falls into your lap, and you are fast asleep.
-- Relative to you, the book is not moving at all.
-- Relative to the seat, you are not moving at all.
-- Relative to the wall and the window, the seat is not moving at all.
-- But your seat is in a passenger airliner. Relative to people on the
ground, you are moving past them at almost 500 miles per hour !
-- Relative to the center of the Earth, the people on the ground are moving
in a circle at more than 700 miles per hour.
-- Relative to the center of the Sun, the Earth and everything on it are moving
in a circle at about 66,700 miles per hour !
How fast are they REALLY moving ?
There's no such thing.
It all depends on what reference you're using.
Answer:
You could use newton’s second law to calculate the force applied to an object if you knew the objects mass and its <u>acceleration.</u>
Explanation:
By, Newtons second law, the force applied on an object directly varies with the acceleration caused and the mass of the object.
This is given by :
Where 
represents force applied on the object , 
represents mass of the object and 
represents the acceleration.
In order to calculate force applied on object we require the mass of the object and its acceleration. The force can be calculated by finding the product of mass and acceleration of the object.
Answer:
The ball fell 275.625 meters after 7.5 seconds
Explanation:
<u>Free fall
</u>
If an object is left on free air (no friction), it describes an accelerated motion in the vertical direction, powered exclusively by the acceleration of gravity. The formulas needed to compute the different magnitudes involved are
Where 
is the final speed of the object in free fall, assumed positive downwards, t is the time elapsed since the release and y is the vertical distance traveled by the object
The ball was dropped from a cliff. We need to calculate the vertical distance the ball went down in t=7.5 seconds. We'll use the formula
The only vertical forces are weight and normal force, and they balance since the surface is horizontal. The horizontal forces are the applied force (uppercase F) in the direction the block slides and the frictional force (lowercase f) in the opposite direction.
Apply Newton's 2nd Law in the horizontal direction:
ΣF = ma
F - f = ma
where f = µmg
F - µmg = ma
F = m(a +µg)
F = (20 kg)(1.4 m/s² + 0.28(9.8 m/s²)
F = 83 N
