Newtons law, interacting objects question?

In summary, the conversation is about a problem involving two blocks with different masses and coefficients of friction on a horizontal table. The goal is to determine the magnitude of forces and acceleration for each block when a constant horizontal force is applied to the lower block. The question asks for a free body diagram and equations to solve the problem. The key is to use the static coefficient of friction to determine the starting force and the kinetic coefficient of friction to determine the movement.
  • #1
Xinio64
4
0
Newtons law, interacting objects question??

A block of mass 5.00 Kg sits on top of a second block of mass 15.0 Kg, which in
turn sits on a horizontal table. The coefficients of friction between the two blocks are
: μs = 0.300 and μk = 0.100. The coefficients of friction between the lower block and
the table surface are: μs = 0.500 and μk = 0.400. You apply a constant horizontal
force to the lower block so that this force is just large enough to make this block start
sliding out from between the upper block and the table.

(a) Draw the free body diagram for each block, naming the forces on each of them.
(b) Determine the magnitude of each force on each block at the instant you have
started pushing but motion has not started.
(c) Determine the acceleration you measure for each block.
 
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  • #2
Welcome to PF!

Hi Xinio64! Welcome to PF! :smile:

You must tell us how far you've got, so that we know what's troubling you, and how to help.

What have you tried? have you drawn the diagram?

What equations have you got? :smile:
 
  • #3
tiny-tim said:
Hi Xinio64! Welcome to PF! :smile:

You must tell us how far you've got, so that we know what's troubling you, and how to help.

What have you tried? have you drawn the diagram?

What equations have you got? :smile:

Well I drawn two free body diagrams, one representing each block. The upper block has a weight and normal force of of 49N and a static frictional force pointing to the right. The lower block has a weight and normal force of 196N and a static frictional force of 78.4N pointing to the left and a constant force F pointing to the right. I don't know if in the free body diagrams I use kinetic friction or static friction forces. Equations I guess is F=ma. That's all I have.
 
  • #4
Xinio64 said:
I don't know if in the free body diagrams I use kinetic friction or static friction forces. Equations I guess is F=ma. That's all I have.

Hi Xinio64! :smile:

To get the starting force, you must use the static coefficient.

To get the movement, you use the kinetic coefficient (but of course you use the force you got from the static coefficient).

So … what value force do you get, and how do you carry on from there? :smile:
 

1. What are Newton's three laws of motion?

Newton's first law states that an object will remain at rest or in motion at a constant velocity unless acted upon by an external force. The second law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. The third law states that for every action, there is an equal and opposite reaction.

2. How do Newton's laws apply to interacting objects?

Newton's laws apply to interacting objects by explaining how forces affect the motion of the objects. When two objects interact with each other, they exert equal and opposite forces on each other, as stated in Newton's third law. These forces can affect the motion of the objects according to Newton's second law.

3. What is the difference between action and reaction forces in Newton's third law?

Action forces are the forces that act on an object, while reaction forces are the forces that result from an object's interaction with another object. In Newton's third law, these forces are equal in magnitude and opposite in direction, exerted by two interacting objects on each other.

4. How does Newton's first law explain the concept of inertia?

Newton's first law states that an object will remain at rest or in motion at a constant velocity unless acted upon by an external force. This means that objects have a tendency to resist changes in their state of motion, known as inertia. The greater the mass of an object, the greater its inertia.

5. Can Newton's laws be applied to non-inertial frames of reference?

Yes, Newton's laws can be applied to non-inertial frames of reference, but additional forces, known as fictitious forces, must be included. These forces arise due to the acceleration of the reference frame and are necessary for the laws to hold true in non-inertial frames of reference.

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