Friction on Aluminum & Copper Blocks: Find Sum of Magnitudes

  • Thread starter Ondra
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In summary: The equation you are looking for is F = µ1m1g + µ2m2g, which is the standard equation relating to static friction.
  • #1
Ondra
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Homework Statement


A 2.00-kg aluminum block and a 6.00-kg copper block are connected by a light string over a frictionless pulley. They sit on a steel surface as shown in Figure P5.64, where theta= 30.0°. When they are released from rest, will they start to move? If so, determine (a) their acceleration and (b) the tension in the string. If not, determine the sum of the magnitudes of the forces of friction acting on the blocks.

https://drive.google.com/file/d/0B4ksjSfetGUOeUdXX0tKODRWVjg/view?usp=sharing ---- IMAGE
fyzika.png


Homework Equations


1) I don't know how to calculate the last part: "If not, determine the sum of the magnitudes of the forces of friction acting on the blocks."

2) Is it so far correctly calculated?

The Attempt at a Solution


For the system to start to move when released, the force tending to move m2 down the incline, m g 2 sinθ, must exceed the maximum friction force which can retard the motion:

F = f(steel) + f(copper)

= µ1m1g + µ2m2g

= 0.61 x 2.0 x 9.8 + 0.53 x 6.0 cos(30) x 9.8 = 38.9 N

Force tending to cause the system to move = 6.0 x 9.8 x sin(30) = 29.4 N
Hence it will not start to move when released.
 
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  • #2
It just hit me... Did I already solved the: "If not, determine the sum of the magnitudes of the forces of friction acting on the blocks." Part? :D
 
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  • #3
Ondra said:
µ2m2g
That is not correct for the block on the slope, but I see you used the right version in the next line.
Ondra said:
Did I already solved the: "If not, determine the sum of the magnitudes of the forces of friction acting on the blocks." Part?
Possibly. You calculated two forces. Which one are you suggesting as answer to part b?
Before answering, what exactly is the standard equation relating to static friction?
 
  • #4
The formula for friction is F = coeffiicent of friction * Normal contact force. For M2, the normal contact force is not the weight. but you have corrected it lol. Where did you get the coefficients from? Online? I see its 0.61 between aluminium and steel.

Also, I know I posted in your earlier thread that got deleted, so please try to check out these two websites:

scroll down for mechanics:
http://www.cimt.org.uk/projects/mepres/alevel/alevel.htm
 
  • #5
Bipolar Demon said:
The formula for friction is F = coeffiicent of friction * Normal contact force.
Not quite, and that is important here.
 
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FAQ: Friction on Aluminum & Copper Blocks: Find Sum of Magnitudes

What is friction?

Friction is the force that resists the relative motion between two surfaces that are in contact with each other.

What causes friction?

Friction is caused by the irregularities on the surface of an object, which create resistance against the motion of another object in contact with it.

How is friction measured?

Friction is typically measured using a device called a friction tester, which applies a known force to the object and measures the force required to move it.

What is the difference between static and kinetic friction?

Static friction is the force that resists the initial motion between two surfaces, while kinetic friction is the force that resists the motion of two surfaces that are already in motion.

How does the type of material affect friction?

The type of material can affect friction as different materials have different roughness and surface properties, which can result in varying levels of friction.

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