The answer is A. 50 m/s
I took the test and completed the study guide in class and got it correct.
Answer:

Explanation:
It is given that,
Mass of the clock, m = 108 kg
Force acting on it when it is in motion, 
After the clock is in motion, a horizontal force of 521 N keeps it moving with a constant velocity, F' = 521 N
It is assumed to find the coefficient of between the clock and the floor. The force of friction is given by :




So, the coefficient of static friction between the clock and the floor is 0.6. Hence, this is the required solution.
The correct answer is
A) true
In fact, the electrical force can be present only if the two objects have a net charge different from zero, because the electrical force is proportional to the value of the charges:

so, if they are neutral they cannot exert an electrical force between each other, because their charge Q is zero.
Viceversa, the gravitational force is always present when the objects have masses, since the force is proportional to the value of the masses:

so, even if the two objetcs are neutral, if they have mass, they exert a gravitational force to each other.
Looks like you need to review through the lesson and take notes as it tells you in the lesson what each of these are.