How to find acceleration given two masses , an angle ,and kinetic fric

[Sneakatone]

Two masses m1=3.2 kg and m2=4.7 kg are connected by a thin string running over a massless pulley. One of the masses hangs from the string , the other mass slides on a 35 degree ramp with a coefficient of kinetic friction uk= 0.30. What is the acceleration of the masses?

I used 9.81(4.7-3.2[0.3cos(35)-sin(35)]/(3.2+4.7)=7.13 but its wrong

 

[JCS2080]

...wonder if instead of trying to deflect coming asteriods away from earth, if instead we can deflect them towards Venus (similar size planet) so to activate a magnetic field and end its runaway greenhouse effect atmosphere. Two Earths are better than one...of course we would need to get a moon there somehow

 

[Sneakatone]

??

 

[Bananas40]

I think (g(m1sen35º-m1cos35ºuk+m2))/(m1+m2) should do the trick.

 

[Sneakatone]

would I need to convert to any specific units? like mm to m, g to kg?

 

[Sneakatone]

I did (9.81(3.2sin(35)-3.2cos(35)(0.3)+4.7))/(3.2+4.7)=7.13
and it is wrong

 

[xk_id]

Does it tell you which mass is on which end of the string?

 

[Sneakatone]

yea m2 is hanging at the end of the string

 

[xk_id]

I did (9.81(3.2sin(35)-3.2cos(35)(0.3)+4.7))/(3.2+4.7)=7.13
and it is wrong

No, it gives -6.46, i.e the masses accelerate in the other direction.

 

[Sneakatone]

If your saying the answer for acceleration is -6.46 then its wrong.

 

[xk_id]

Try 6.46?

 

[Sneakatone]

that is also incorrect.

 

[haruspex]

I did (9.81(3.2sin(35)-3.2cos(35)(0.3)+4.7))/(3.2+4.7)=7.13
and it is wrong

You have a sign wrong. Think about which way the forces on m1 parallel to the ramp act.

 

[Sneakatone]

I switched cos with sin n I got 8 which is wrong

 

[haruspex]

I switched cos with sin n I got 8 which is wrong

Wrong correction. List the forces acting on m1 parallel to the ramp. What are their magnitudes? Which ones act in the direction of acceleration and which oppose it? What does that make the net force producing the acceleration?

 

[Bananas40]

Oh, sorry, I misunderstood the first post.

Try this equation for the acceleration:

(g[-m₁sin35°-m₁cos35°μ_k+m₂])/(m₁+m₂)

It gives 2,58 m/s^2

 

[SaxonMilton]

can someone please help with my question now?

 

[Bananas40]

Did my equation work?

 

[lep11]

can someone please help with my question now?

https://www.physicsforums.com/showthread.php?t=675596

 

[haruspex]

Oh, sorry, I misunderstood the first post.

Try this equation for the acceleration:

(g[-m₁sin35°-m₁cos35°μ_k+m₂])/(m₁+m₂)

It gives 2,58 m/s^2

I agree with that.