Questions about forces on surfaces

The lower block will move as far as the upper one in the same time, so you can also determine its displacement. In summary, the problem involves a small block of mass 2 kg and a larger block of mass 8 kg, with a coefficient of kinetic friction of 0.3 between them. A constant horizontal force of 10 N is applied to the small block, causing it to move and in turn exerting a force on the larger block. The upper block will reach the right side of the lower block in a certain amount of time, and the lower block will also move a certain distance in that time.
  • #1
Pseudo Statistic
391
6
I've been trying to go through the problems in our assigned textbook, College Physics, but like any other Serway book the material is not in-depth enough for me to be able to solve the problems easily.
This one particular problem has got me thinking about how blocks would move across a surface when there are two surfaces:
A small block of mass m = 2kg rests on the left edge of a block of length L = 3m and mass M = 8kg. The coefficient of kinetic friction between the two blocks is mu_k = 0.3, and the surface on which the 8kg block rests is frictionless. A constant horizontal force of magnitude F = 10N is applied to the 2kg block, setting it in motion. a) How long will it take before this block makes it to the right side of the 8kg block? (Note: Both blocks are set in motion when F is applied.) (b) How far does the 8kg block move in the process?
My main concern is what kind of a force would be applied on this block with mass M; would it be that exact 10N force or something else?
I'd really appreaciate if someone could shed some light on how one can comprehend a problem such as this, as I can't make sense of the method my teacher used.
Thanks a lot for any replies.
 
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  • #2
Pseudo Statistic said:
My main concern is what kind of a force would be applied on this block with mass M; would it be that exact 10N force or something else?
The applied force is given as 10N, so we must assume that's what it is! :smile:

Now, to understand how each mass will accelerate and move, we have to look at all the forces acting on each. The top block has two forces acting on it, while the bottom block has only one. (Considering only the horizontal forces, since there is no vertical acceleration.)

To figure out when the top block reaches the other side, compare the accelerations of each block.
 
  • #3
Pseudo Statistic said:
I've been trying to go through the problems in our assigned textbook, College Physics, but like any other Serway book the material is not in-depth enough for me to be able to solve the problems easily.
This one particular problem has got me thinking about how blocks would move across a surface when there are two surfaces:
A small block of mass m = 2kg rests on the left edge of a block of length L = 3m and mass M = 8kg. The coefficient of kinetic friction between the two blocks is mu_k = 0.3, and the surface on which the 8kg block rests is frictionless. A constant horizontal force of magnitude F = 10N is applied to the 2kg block, setting it in motion. a) How long will it take before this block makes it to the right side of the 8kg block? (Note: Both blocks are set in motion when F is applied.) (b) How far does the 8kg block move in the process?
My main concern is what kind of a force would be applied on this block with mass M; would it be that exact 10N force or something else?
I'd really appreaciate if someone could shed some light on how one can comprehend a problem such as this, as I can't make sense of the method my teacher used.
Thanks a lot for any replies.

The upper block exerts on the lower one a force of f = mg Newtons, so there is a friction of f*mu_k between the two blocks. It is this force that moves the lower block. Since the upper one is acted upon by a force of 10 N, you can calculate their respective accelerations and the time the upper block will take to cover the distance of 3 m.
 

1. What is a force?

A force is a push or pull that can cause an object to move, accelerate, or change direction. It is a vector quantity, meaning it has both magnitude and direction.

2. What are the types of forces that act on surfaces?

The types of forces that act on surfaces are normal force, frictional force, tension force, and shear force. Normal force is perpendicular to the surface and helps keep objects in place. Frictional force opposes the motion of an object on a surface. Tension force occurs when an object is being pulled outward from both ends. Shear force acts parallel to the surface and can cause objects to slide or deform.

3. How do forces on surfaces affect motion?

Forces on surfaces can affect motion in various ways. They can cause an object to move, change speed, change direction, or stay at rest. The specific effect depends on the magnitude and direction of the force, as well as the mass and shape of the object.

4. How can we calculate the net force on an object on a surface?

The net force on an object on a surface can be calculated by summing up all the forces acting on the object. If the forces are in the same direction, you can simply add them together. If they are in opposite directions, you can subtract the smaller force from the larger one. The resulting force will determine the motion of the object.

5. How does surface area affect the forces acting on an object?

The surface area of an object can affect the forces acting on it in several ways. A larger surface area can increase the amount of frictional force, making it harder to move an object. It can also increase the amount of air resistance, which can slow down the motion of an object. On the other hand, a smaller surface area can decrease the amount of air resistance, making it easier for the object to move through air. It can also decrease the amount of frictional force, making it easier to slide an object on a surface.

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