1) which force is always perpendicular (90 degree angle) to a surface. so, if you are sitting on the floor, what is the name of the force "the floor pushes up on you"?
a) normal
b) friction
c) weight
d) tension

2) which of these statements is always true?
a) a moving object in equilibrium can change its direction but not its speed.
b) if an object is moving, a net force is acting on it.
c) an object in equilibrium must not be in motion.
d) a moving object in equilibrium continues at a constant velocity.

3) choose the force that always acts opposite the direction of the motion. so, if a car is moving forwards, what force would act backwards?
a) friction
b) weight
c) applied
d) normal

4) which of these would you include in a free body diagram of a coin sitting on a table?
a) the table
b) the forces of the coin pushing down on the table
c) room, to depict the physical setting
d) the force of gravity (weight) acting on the coin

Answers:

1) The answer is A, the Normal Force. This is the force exerted by a surface on a body resting on it.

This force is a good example of Newton’s third law (Action and Reaction), in which the force exerted by the floor on you is the same in magnitude but in opposite direction to the force exerted by the weight of your body sitting on the floor.

2) The first Newton Law of Motion states that an object at rest or describing a uniform straight line motion (moving at constant velocity), will remain at rest or moving unless a force is applied to it and changes its state of rest or motion.

This means that objects tend to remain in its state of motion or rest until a force is exerted on them.

According to his law, an object in rest can be in equilibrium (net force equals to zero), and a moving object can also be in equilibrium, as long as it keeps a constant velocity.  

Therefore, the right answer is D

A moving object in equilibrium continues at a constant velocity

3) The right answer is friction, the force that resists the motion of an object and fulfills the condition of acting in opposite direction to the motion of the object.

4) In this case, the weight of the coin must be included in the free body diagram, taking into account that in these diagrams are shown in a vector and simple way the magnitudes and respective directions of all forces exerted on an object.  

Then, elements such as the table or the room itself don’t give relevant information of the forces acting on the coin.

Therefore, the answer is D the force of gravity (weight) acting on the coin

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