Answer:
a. A baseball after it has been hit - not in free fall
b. A rock that is thrown in the air - not in free fall
c. The moon - free-fall
d. A paper airplane - not in free fall
e. A bird flying - not in free fall
Explanation:
- The free-fall is defined as the falling of an object due to the action of gravity. The object is not experiencing any other force neglecting the air resistance.
- If an object is in free-fall, the direction of its motion is directed towards the center of the earth. It does not have a horizontal component of velocity.
- If the body is under free-fall, but a centripetal force acts on it where it is equal to the gravitational force at that point. The object will have two components of velocity along the tangential line, perpendicular to the radius of the orbit.
a. A baseball after it has been hit - not in free fall according to point 1 & 2.
b. A rock that is thrown in the air - not in free fall according to point 1.
c. The moon - free-fall according to point 3.
d. A paper airplane - not in free fall according to point 1 & 2.
e. A bird flying - not in free fall according to point 1 & 2.
Such information is valid when A. it is not biased.
There is no bias in science - the results are either correct or incorrect; personal opinions have nothing to do with that. B is incorrect because the point of experiments is that they can be repeated to achieve the same results. C and D are likewise incorrect as primary sources are important, and you can share the results with others if you want to.
I think the answer would be letter B.
1) 12.5 N east
There are two forces acting on the box along the horizontal direction:
- The applied force of 15 N east, we indicate it with F
- The force of friction of 2.5 N west, we indicate it with 
Taking east as positive direction, we can write the two forces has
Therefore, the net force on the box will be:
And the positive sign means the direction is east.
2) 
We can solve this part by using Newton's second law:
where
is the net force on the box
m is its mass
a is the acceleration
For the box in this problem,
(east)
m = 5.0 kg
Solving for a, we find the acceleration:
And the direction is the same as the net force (east)
