Normal force, friction force, gravitational force
Explanation:
Cold butter placed on hot corn melts because of convection. Butter placed on hot corn melts because it touches the hot corn. Most of the heat is transferred through conduction
Without being provided a list of items, I would have to generally say that everything around you is matter. There are a few exceptions to this list, but a general rule of thumb is anything you can touch, taste, smell or hold would be considered matter. Sound, light, time (Dr. Who may disagree) and heat would be considered non-matter items.
To solve this problem we will use the linear motion description kinematic equations. We will proceed to analyze the general case by which the analysis is taken for the second car and the tenth. So we have to:

Where,
x= Displacement
= Initial velocity
a = Acceleration
t = time
Since there is no initial velocity, the same equation can be transformed in terms of length and time as:

For the second cart

When the tenth car is aligned the length will be 9 times the initial therefore:

When the tenth car has passed the length will be 10 times the initial therefore:

The difference in time taken from the second car to pass it is 5 seconds, therefore:

From the first equation replacing it in the second one we will have that the relationship of the two times is equivalent to:


From the relationship when the car has passed and the time difference we will have to:



Replacing the value found in the equation given for the second car equation we have to:

Finally we will have the time when the cars are aligned is


The time when you have passed it would be:


The difference between the two times would be:

Therefore the correct answer is C.
The angle between the string and the vertical is computed by:
Centripetal acceleration Ac = V²/R = 18²/75 = 4.32 m/s² horizontal
Gravitational acceleration g = 9.8 m/s² down
Θ = arctan(Ac/g)
= arctan (4.32m/s^2 / 9.8 m/s^2)
= 23.79° is the answer.