Forces and Free-Body Diagrams

The free-body diagram shown for an object being pushed to the right across a rough floor at a constant speed has what wrong with it?

• The friction force should be in the same direction as the applied force.

• The applied force should be the same size as the friction force.

• The normal force should be larger than the force of gravity.

• There is nothing wrong with this free-body diagram.

Tags

NGSS.MS-PS2-2

Look at the following steps for drawing a free-body diagram, and determine what Step 4 should be:

Step 1: Draw a simple shape for the object

Step 2: Identify all of the forces acting on the object

Step 3: Draw an arrow for each force acting on the object pointing in the right direction

• Draw in an arrow for the net force

• Calculate the acceleration using the mass of the object

• Draw all of the objects that are pushing / pulling at the ends of the arrows

• Make sure the length of each arrow correctly represents the strength of the force

A student is analyzing the forces on a 400 kg car driving at a constant velocity of 20 m/s. What is wrong with the student's force diagram?

• The forward force should be 20 N rather than 8000 N since F_net = m·a

• The diagram shows a net force but the net force on the car should be zero

• There cannot be any forces on the car if it has a constant velocity so there should be no arrows

• There should be more backward force on the car because the care is slowing down

Tags

NGSS.MS-PS2-2

Which of the arrows in this diagram represents the normal force acting on the box?

• Arrow A

• Arrow B

• Arrow C

• Arrow D

A 2 kg block slides down a rough 30° inclined plane as shown in the picture. The block has an acceleration of 2 m/s². Which diagram BEST shows the force of gravity (W), the friction force (f), and the normal force (N) acting on the block?

• 
• 
• 
• 

Tags

NGSS.HS-PS2-1

A box is being pushed up a ramp at constant velocity into a moving truck. Which of these statements correctly describes the free-body diagram for the box?

• The weight is pulling straight down, and the normal force is directed straight up. Since it is moving at a constant velocity, there are no forces acting along the ramp.

• The weight is pulling straight down, and the normal force is directed perpendicular to the surface. Since it is moving at a constant velocity, there are no forces acting along the ramp.

• The weight is pulling straight down, and the normal force is directed straight up. Since it is moving at a constant velocity, there are equal and opposite forces acting along the ramp.

• The weight is pulling straight down, and the normal force is directed perpendicular to the surface. Since it is moving at a constant velocity, there are equal and opposite forces acting along the ramp.

Tags

NGSS.MS-PS2-1

NGSS.MS-PS2-2

The force that keeps objects on top of surfaces instead of letting them sink into the surface is known as:

• normal

• abnormal

• static

• inertia

Calculate the net force for the diagram.

• 800 N down unbalanced

• 600N down balanced

• 400 N down unbalanced

• 400 N up unbalanced

Tags

NGSS.MS-PS2-2

A person stands on a scale in an elevator. If the elevator accelerates upward, what happens to what the scale reads (i.e. the normal force)?

• It increases.

• It stays the same.

• It decreases.

• It changes to a negative value.

Tags

NGSS.MS-PS2-1

NGSS.MS-PS2-2

As the angle of the incline increases, what happens to the normal force?

• The normal force increases

• The normal force decreases

• The normal force is not affected by the incline

• The normal force is only dependent on the force due to gravity

Tags

NGSS.HS-PS2-1