Multiple choice but no answers to them so can't study?

[rickkwa]

I'm studying for a test tomorrow, I found these multiple choice questions but no answers to them. If you can help me out so I know which one is correct so I can study properly, that would be much appreciated :D


1. A 24-kg traffic light is suspended from the midpoint of a cable suspended between 2 poles. The angle between the cable and the pole is 80 degrees at both poles. The net force acting on the traffic light has a value of:
a. zero // this one maybe?
b. 47 N
c. 82 N
d. 2.4 x 10^2 N
e. 4.6 x 10^2 N

2. Is this an example of inertia?
A person is largely unaware of a car's motion when his eyes are closed.
// I want to say no..

3. With respect to Newton's third law, the action and reaction forces:
a. being equal, imply a "balanced" force situation
b. act on different objects
c. are equal provided the object is at rest
d. are equal provided the object is moving with uniform motion
e. are equal provided the object is NOT at rest or moving with uniform motion

4. A 4-kg object, A, and a 2-kg object, B, are connected with a rope. A force is applied to another rope attached to the 2-kg object that pulls both A and B along a horizontal surface. Which of the following statements is true?
a. The force that B exerts on A is greater than the force that A exerts on B
b. The force that A exerts on B is greater than the force that A exerts on B
c. The force that B exerts on A is equal to the force that A exerts on B provided that the system slides with uniform motion
d. The force that B exerts on A is equal to the force that A exerts on B regardless of the motion of the system
e. The sum of the applied force and the force that B exerts on A is equal to the force that A exerts on B

5. An object is pushed horizontally at a constant velocity. What can correctly be said about the forces acting on the object?
a. The force(s) acting forward is/are greater than the force(s) acting backward
b. The sum of all the forces has a value directed forward
c. The sum of all forces is zero
d. The forces acting on the object can be said to be "unbalanced"
e. Newton's second law best summarizes the effect of the forces acting on the object

6. An elevator is moving upward at a constant velocity. What is the relationship between the gravitational force (Fg) acting on the elevator and the tension (Ft) in the cable that supports the elevator?
a. Fg = Ft
b. Fg > Ft
c. Fg < Ft
d. Fg >= Ft
e. Fg <= Ft

7. Three identical masses are suspended vertically. There are strings between the masses to hold them together. There is also a string to hold the topmost mass. The system is accelerating upward. What is the relationship among the forces of tension? Ft1, Ft2, Ft3 are the tensions. Ft1 being on top.
a. Ft1 = Ft2 = Ft3
b. Ft1 > Ft2 > Ft3 // I am thinking its probably this one
c. Ft1 < Ft2 < Ft3
d. Ft1 > Ft2 < Ft3
e. Ft1 > Ft3 < Ft2

8. An object sits at rest on a ramp. As the angle of inclination of the ramp increases, the object suddenly begins to slide. Which of the following explanations best accounts for the object's movement?
a. The coefficient of static friction has decreased sufficiently
b. The force of gravity acting on the object has increased sufficiently
c. The component of gravity along the ramp has increased sufficiently // This is my best bet
d. The friction has decreased sufficiently while the normal force has remained unchanged
e. The formal force has increased sufficiently

 

[Pengwuino]

Giving you the answer is not proper studying. Show some work on a question and people will help you.

 

[rickkwa]

Well I am asking this because I have no idea. My teacher doesn't teach properly, he skips all this stuff and goes right into problems. So these multiple choice are hard for me. there's not much work I can show. If I had some answers or hints, I can at least get rid of some of the confusion I have about those tension questions. You can't at least give me hints or resources?

 

[Pengwuino]

Well for the first problem, if the traffic light DID have a net force on it, that would mean it would accelerate correct? The fact that it's suspended (and implied that it's not jumping around) does mean there is no acceleration which is what you have. Does that make sense?

The second question is probably better understood with a train. Have you ever ridden a very smooth train? A smoothly riding train, if it had no windows, would be indistinguishable from a train at rest. This is because every aspect of the train and you as a rider are traveling at the same velocity and have inertia. Unless there were an acceleration from say, a braking or accelerating to a higher speed, you will all continue along with no clue as to what the speed of the train really were. So yes, in a sense, inertia is the reason a person in a car with constant velocity is relatively unaware of the car's motion.

For the third question, can you think up situations that would help you figure this one out?