Pulley and Friction: Solving for Mass and Acceleration on an Inclined Plane

In summary: I'm stuck. Will try again later."In summary, if the masses were at rest and then someone added 2.8 kg to m2, the masses would begin to move.
  • #1
Coco12
272
0

Homework Statement



m1 has a mass of 47 kg and m2 has a mass of 35 kg. the coefficient of friction between m1 and the surface of the inclined plane are us=.42 and uk=.19 m1 is on an inclined plane angled 25 degrees

A) if the masses are held in place and then released, will they start to move?
B) what mass would you have to add to m2 to cause the masses to begin to move?
C) what would be the acceleration of the masses after adding the additional mass?

Homework Equations


For b- made fnet equal to 0 and solved for m2. (37.8) subtracted 37.8 from 35 to get 2.8kg of additional mass

For c- I used fnet=ma fnet= -Ff-fparallel+m2g/m1+m2
However I didn't get the right answer??

The Attempt at a Solution


I know the answer for a is no.. But how do u determine that it's a no? Is it if Ff + f parallel is more than Ft?
For c.. The answer is 5.7m/s2, how do u get that??
 
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  • #2
"I know the answer for a is no.. But how do u determine that it's a no?"
1. ASSUME that they are at rest.
2. From this, calculate what the magnitude of the frictional force must be.
3. Compare this value with the MAXIMAL value static friction can have. If the force from 2. exceeds that, it means the objects must move instead. Otherwise, if the solution in 2. is less than the maximal value the static friction can have, then the objects are at rest.
 
  • #3
arildno said:
"I know the answer for a is no.. But how do u determine that it's a no?"
1. ASSUME that they are at rest.
2. From this, calculate what the magnitude of the frictional force must be.
3. Compare this value with the MAXIMAL value static friction can have. If the force from 2. exceeds that, it means the objects must move instead. Otherwise, if the solution in 2. is less than the maximal value the static friction can have, then the objects are at rest.


Do u mean take the kinetic friction and compare it to static?
 
  • #4
Coco12 said:
Do u mean take the kinetic friction and compare it to static?
No.
Call your friction "f", and see what the system at rest implies that the magnitude of "f" must be.
THEN compare it to the maximal value for static friction.
 
  • #5
arildno said:
No.
Call your friction "f", and see what the system at rest implies that the magnitude of "f" must be.
THEN compare it to the maximal value for static friction.

U mean set fnet = 0 and solve for Ff?



Also do u understand how to do c?? I'm stuck on it. Thanks
 
  • #6
"fnet = 0 and solve for Ff"
Quite so! :smile:

Then, you'll get a value for F.f
If that value exceeds the maximum static friction can have, your solution is INCONSISTENT with the premises, meaning the system had to be moving after all.
If, however, F-f's value is LESS than maximum value, system at rest is the correct solution.
 
  • #7
Thank you :).. As for question c?
 

1. What is a pulley?

A pulley is a simple machine that consists of a wheel with a groove around its circumference, used to change the direction of a force and provide mechanical advantage in lifting or moving objects.

2. How does a pulley work?

A pulley works by using a rope or cable to support a load and applying force to one end of the rope to lift or move the load. The pulley's grooved wheel reduces the amount of force needed to lift the load by distributing it over multiple strands of rope or cable.

3. What is friction and how does it affect pulleys?

Friction is a force that resists motion between two surfaces in contact. In the case of pulleys, friction can affect the efficiency of the machine by causing the rope or cable to slip or creating resistance that requires more force to overcome.

4. How can friction be reduced in pulley systems?

To reduce friction in pulley systems, lubricants such as oil or grease can be applied to the moving parts. Using pulleys with bearings can also help reduce friction. Additionally, ensuring that the pulleys are clean and free of debris can help reduce friction.

5. What are some real-world applications of pulleys and friction?

Pulleys and friction are commonly used in many industries, such as construction, transportation, and manufacturing. Examples of real-world applications include cranes and elevators that use pulleys to lift heavy objects, conveyor belts that use friction to move materials, and car engines that use pulleys and friction to power various components.

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