3.2.1 Free-Body Diagrams Flashcards
Free-Body Diagrams
• When using Newton’s second law:
1. Focus on one object, and consider all the forces acting on it.
2. Draw a free-body diagram (or force diagram).
3. Choose a coordinate system
• A free-body diagram is a rough sketch of an object and the forces applied to it.
Which of the following correctly describes force diagrams?
Force diagrams allow you to calculate force, but not velocity.
The force diagram shows a weight sitting motionless on a table. It has two forces acting upon it: the weight of the object pushing down and the force of the table pushing up. Given that the sum of the forces must equal zero, which of the following is correct?
FOT - mg = 0
The force diagram shows a weight sitting motionless upon a table. Newton’s second law tells us that this diagram is incomplete. Which of the following best explains why it is incomplete?
Because the object is motionless, the kinematic side of the equation must equal zero, Fnet = 0. In the diagram, however, a net force of the object’s weight is pushing downward, indicating an acceleration in the downward direction. There must be another force in the direction opposite to the object’s weight to cancel out the downward acceleration
The following answer choices describe a sequence of steps used by scientists when applying Newton’s second law during experiments. Which of the following would not be used when applying Newton’s second law?
Choose a group of objects to observe.
The diagram shows a coffee filter falling to the ground. Given that
Fnet = 0,
Fairdrag + W = 0, and
Fairdrag - mg = 0,
hwich of the following best describes the motion of the filter
The filter is moving downward at a constant velocity.
The attached diagram shows a weight sitting motionless on a table.
It has three forces acting upon it. The first is the weight of the object pushing down (W); the second is the force of a man pushing down on it with his hand (FOM); the third is the force of the table pushing up (FOT). The sum of the three forces is zero, and can be expressed as the equation FOT + FOM + W = 0. Given that FOT is in the positive direction, which of the following correctly restates this equation as a vector equation and as a value for FOT?
FOT = -FOM - W FOT = Fom + mg
When drawing a free-body diagram, ____________.
consider one object and all the forces acting on that object
On an icy stretch of interstate highway, two cars move out of their lanes and simultaneously collide with an sport-utiltiy vehicle (SUV) parked on the shoulder.
Which of the following contains an equation that would not help us determine the resulting acceleration of the SUV?
C1y + C2y = ma
The diagram shows a box of books being pushed by two students on an icy surface. Assume that friction is negligible. One student is applying a force (F1) to the box at an angle and the other student is applying a force (F2) to the box at another angle. Based on this information, equation can be written to calculate the acceleration of the box. Which of the following is an equation that would not help you determine the acceleration of the box?
a = ax - ay
