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-PS2-1

NGSS.MS-PS2-2

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

• 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

Draw a free body diagram for a car moving at a constant velocity on a straight road. Which forces should be included?

• Only gravitational force

• Gravitational force and normal force

• Gravitational force, normal force, and frictional force

• Gravitational force, normal force, frictional force, and applied force

Tags

DOK Level 2: Skill/Concept

Label a free body diagram for a book attached to a string.

a

b

F air

F tens

F norm

F grav

Tags

NGSS.MS-PS2-4

A 10 kg object is at rest on a horizontal surface. A horizontal force of 30 N is applied, and the object accelerates at 2 m/s². What is the frictional force acting on the object?

• 10 N

• 20 N

• 30 N

• 50 N

Tags

DOK Level 3: Strategic Thinking

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

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