Two blocks, a pulley, and an inclined plane.

In summary, the conversation discusses a physics problem involving an 8kg block on an inclined plane connected to a hanging 16kg block by a pulley. Using the equation F=ma, the attempt at a solution resulted in an acceleration of 3.97. However, after checking the answer, it was stated that the correct acceleration is 1.3 and the participants are unsure of what they may be doing wrong.
  • #1

Homework Statement


An 8kg block rests on an inclined plane where theta=37 degrees. The coefficient of kinetic friction on the plane is .23. The 8kg block is connect by a massless, frictionless pully to a hanging 16kg block. The blocks are released from rest. What is the acceleration.


Homework Equations



I think F=ma

The Attempt at a Solution



So I used F=ma for each block.

8kg block.

T-sin(37)*8*9.8-cos(37)*8*9.8*.23=8*a eq1

16kg block.

T-9.8*16=-16*a eq2

so eq1-eq2 =

9.8*16-sin(37)*8*9.8-cos(37)*8*9.8*.23=24a.

so 95.2=24a

leaving a=3.97.

When we checked the answer it said a = 1.3. What are we doing wrong?
 
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  • #2
I also got 3.97.
 
  • #3
Agreed. I spent a few minutes checking if there was a transcription error ([itex]\theta=90-37[/itex], transposed masses, both of the above) and I can't get 1.3. The best I can do is that a coefficient of friction of 1.23 gets you an acceleration of 1.36ms^-2, and you'd have to coat the ramp in glue to get that.

Unless someone answers with something that we're all doing wrong, I'd just double check that you haven't mis-read something in the question and hand it in.
 
Last edited:

1. How does a pulley affect the motion of two blocks?

A pulley can be used to change the direction of the force applied to the blocks. It can also increase or decrease the force needed to move the blocks, depending on the configuration of the pulley system.

2. What is the purpose of using an inclined plane in this setup?

The inclined plane allows for the blocks to be moved with less force than if they were being lifted straight up. It also allows for the force needed to be spread out over a longer distance, making it easier to move the blocks.

3. Can the direction of the inclined plane affect the motion of the blocks?

Yes, the direction of the inclined plane can affect the motion of the blocks. If the plane is angled upwards, it will require more force to move the blocks. If it is angled downwards, it will require less force.

4. How does the weight of the blocks affect their motion on the inclined plane?

The weight of the blocks will affect the force needed to move them on the inclined plane. Heavier blocks will require more force to move up the plane, while lighter blocks will require less force.

5. Is there a specific way to arrange the pulley system to make it easier to move the blocks?

Yes, using a combination of fixed and movable pulleys can make it easier to move the blocks. This allows for the weight of the blocks to be distributed between multiple ropes and pulleys, reducing the overall force needed to move them.

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