Block Moving Down A Moving Wedge

In summary: They may be helpful.I have looked at the links and they are all helpful. Thank you.Have you looked at the links and they are all helpful. Thank you.
  • #1
GnG.Vike13
11
0

Homework Statement



A mass of 5kg and wedge of 10kg are held at rest. All surfaces are frictionless. No outside forces are acting on the system. θ of the wedge is 30°. Once the block and wedge are let go, what happens to both objects? What is the acceleration of the block left/right and what is the acceleration of the block down the wedge?

Homework Equations



I seriously do not get this problem at all.

The Attempt at a Solution



When I made a fbd, and split both masses into x and y components, it showed that the wedge will accelerate in the opposite direction of the block's acceleration.

Anyone understand this?
 
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  • #2
GnG.Vike13 said:
... anyone? I just don't why the block will continue to move along with the wedge if the wedge goes backwards.
Why not? The block slides down the wedge, pushing the wedge backwards. If you viewed their motion with respect to the ground, how would it look?
 
  • #3
Doc Al said:
Why not? The block slides down the wedge, pushing the wedge backwards. If you viewed their motion with respect to the ground, how would it look?

Thank you for the reply.

I understand that the block will continue to move down along the block... But we had a problem with this concerning conservation of energy. But the work that the block does on the wedge is positive and the work that the wedge does on the block is positive, why is energy conserved? It doesn't make sense.
 
  • #4
Why doesn't it make sense? Don't forget about gravity.
 
  • #5
Because a positive work is acted on in the system. Therefore, energy must've been added to it.
 
  • #6
GnG.Vike13 said:
bump
Please, read the Forum rules regarding bumping.
 
  • #7
Have you looked at the links at the bottom of this web page. This problem has been addressed many times, sometimes quite well.
 
  • #8
GnG.Vike13 said:
Because a positive work is acted on in the system. Therefore, energy must've been added to it.
Once again I will remind you not to forget about gravity.

Also you may want to compare what happens when the wedge cannot move versus when it is free to move (as in this case).
 
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  • #9
I am taking gravity into account. The wedge moves left and the block moves right and down. There is a positive force to the left acting on the wedge and a positive force to the right acting on the block, along with gravity acting down. Therefore, all work done in this problem is positive. Since we area adding positive work into the system, Wnc= delta E
 
  • #10
There is no non-conservative work being done here. The increase in KE of the block and wedge is due to the work done by gravity.
 
  • #11
So, the work done by gravity is shraed between the two objects, correct?

But looking at it from a Newton's Laws perspective, how would you go about solving for the accelerations of each objects? Like, how does the acceleration of the wesdge relate to the acceleration of the block?
 
  • #12
GnG.Vike13 said:
So, the work done by gravity is shraed between the two objects, correct?
Right.

But looking at it from a Newton's Laws perspective, how would you go about solving for the accelerations of each objects? Like, how does the acceleration of the wesdge relate to the acceleration of the block?
Start by identifying the forces acting on each object and draw yourself a FBD of each. (You might have already done that.)

One constraint to apply is that the block maintains contact with the wedge. Call the acceleration of the wedge aw and the acceleration of the block with respect to the wedge a. (aw will be horizontal and a will be parallel to the wedge.)
 
  • #13
SammyS said:
Have you looked at the links at the bottom of this web page. This problem has been addressed many times, sometimes quite well.

Check these out !
 

FAQ: Block Moving Down A Moving Wedge

What is a block moving down a moving wedge?

A block moving down a moving wedge is a simple physics problem that involves two objects in motion: a block sliding down a stationary wedge and the wedge itself moving horizontally. This situation is often used to demonstrate the principles of friction, forces, and motion.

How does the angle of the wedge affect the block's motion?

The angle of the wedge can affect the block's motion in several ways. As the angle increases, the force of gravity pulling the block down the wedge also increases, causing the block to accelerate faster. Additionally, a steeper angle can decrease the contact area between the block and the wedge, resulting in less friction and potentially increasing the block's speed.

What role does friction play in this scenario?

Friction plays a crucial role in this scenario as it is the force that opposes the block's motion down the wedge. Without friction, the block would slide down the wedge at a constant speed. However, as the block moves, it creates friction, which pushes back against the block and slows it down. This friction force is proportional to the normal force between the block and the wedge, which also increases with a steeper wedge angle.

How does the block's mass affect its motion down the wedge?

The block's mass has a direct impact on its motion down the wedge. According to Newton's second law of motion, the acceleration of an object is directly proportional to the force applied to it and inversely proportional to its mass. This means that a heavier block will require more force to accelerate down the wedge compared to a lighter block.

What factors can affect the final velocity of the block?

The final velocity of the block down the wedge can be affected by various factors, including the angle of the wedge, the block's mass, and the coefficient of friction between the block and the wedge. Additionally, external forces such as air resistance or an applied force can also affect the block's final velocity.

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