3.2.3 Solving Problems Using Newton's Laws: Inclines and the Normal Force

Question 1

Solving Problems Using Newton’s Laws: Inclines and the Normal Force

Answer 1

• The normal force (also called the contact force) is the force perpendicular to the contact surface between two objects.
• For problems involving inclines, it’s easiest to choose the x-axis parallel to the inclined plane and the y-axis perpendicular to it.
• There is no formula for the normal force; its magnitude and direction adjusts depending on the physics of the situation so that the object doesn’t pass through the surface.
• On an incline with no friction, the acceleration is gsinq and the normal force is mgcosq, where q is the angle of the incline relative to the horizontal.

Question 2

Which of the following is the correct formula for determining the normal force?

Answer 2

None of the above

Question 3

Look at the diagram showing an object on an incline. The weight of the object is represented by W. Which of the following depicts the correct normal force, N?

Answer 3

-

Question 4

Let theta = 0 degrees be horizontal and pointing toward the right. The following equations describe the accelerations of a cart on a track in two different situations:
1. a = g sin 0 degrees
2. a = g sin 90 degrees
Which fo the following correctly depicts the proper orientation of the track and cart for each equation?

Answer 4

-

Question 5

Physicists and mathematicians describe a certain kind of force as “normal”. Which of the following describes a normal force?

Answer 5

The force of contact between two objects because it is perpendicular to the contact surface between the two objects.

Question 6

Look at the diagram showing a metal cart sitting motionless on an airtrack. The airtrack is on, so you can assume there is no friction. The forces are equal, therefore, there is no net force. Which of the following correctly identifies the normal force in this scenario?

Answer 6

the force of the track on the cart, FOT

Question 7

The diagram shows a roller skate on the incline of a hill. The x-coordinate is parallel to the inclined surface. The roller skate has a mass of 5.00*10^-1 kg and is on a hill with a 30 degree incline. The sine of 30 degrees is 0.5. The cosine of 30 degrees is 0.866. The constant g is equal to 9.8 m/s^2. Which of the following are the values of a and N?

Answer 7

a = 4.9 m/s^2
N = 5.00*10^-1 kg * (9.8m/s^2) * 0.866 = 4.2 kg m/s^2

Question 8

Diagrams A and B show a weight on an incline. Assume that the system has no friction. The x- and y-axes are also shown. Which of the following correctly states the simplest form of the equation needed to determine the acceleration?

Answer 8

a = gsin theta

Question 9

Diagram A shows a weight on an incline. Assume that the system has no friction. The x- and y-axes are also shown. From the orientation of the axes, Fy = 0, there is no motion in the y-direction. To solve for N, you have to determine the value of W (mg). For reference, Diagram B shows the same incline with the x- and y-components of weight labeled. Which of the following is the equation for N?

Answer 9

N = mg cos theta

Question 10

Look at the diagram showing an object on an incline. The weight of the object is represented by W and the normal force by N. The motion of the object in this diagram will occur in two dimensions, therefore, a coordinate system must be defined. Which of the following defines the optimal coordinate system fro problems involving inclines?

Answer 10

The x-axis should be parallel with the inclined surface, with the y-axis parallel to N