# Homework Help: How to find acceleration given two masses , an angle ,and kinetic fric

1. Mar 1, 2013

### 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

2. Mar 1, 2013

### JCS2080

Re: how to find acceleration given two masses , an angle ,and kinetic

....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

3. Mar 1, 2013

### Sneakatone

Re: how to find acceleration given two masses , an angle ,and kinetic

????????????

4. Mar 1, 2013

### Bananas40

Re: how to find acceleration given two masses , an angle ,and kinetic

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

5. Mar 1, 2013

### Sneakatone

Re: how to find acceleration given two masses , an angle ,and kinetic

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

6. Mar 1, 2013

### Sneakatone

Re: how to find acceleration given two masses , an angle ,and kinetic

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

7. Mar 1, 2013

### xk_id

Re: how to find acceleration given two masses , an angle ,and kinetic

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

8. Mar 1, 2013

### Sneakatone

Re: how to find acceleration given two masses , an angle ,and kinetic

yea m2 is hanging at the end of the string

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9. Mar 1, 2013

### xk_id

Re: how to find acceleration given two masses , an angle ,and kinetic

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

10. Mar 1, 2013

### Sneakatone

Re: how to find acceleration given two masses , an angle ,and kinetic

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

11. Mar 1, 2013

### xk_id

Re: how to find acceleration given two masses , an angle ,and kinetic

Try 6.46?

12. Mar 1, 2013

### Sneakatone

Re: how to find acceleration given two masses , an angle ,and kinetic

that is also incorrect.

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13. Mar 1, 2013

### haruspex

Re: how to find acceleration given two masses , an angle ,and kinetic

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

14. Mar 1, 2013

### Sneakatone

Re: how to find acceleration given two masses , an angle ,and kinetic

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

15. Mar 1, 2013

### haruspex

Re: how to find acceleration given two masses , an angle ,and kinetic

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?

16. Mar 2, 2013

### Bananas40

Re: how to find acceleration given two masses , an angle ,and kinetic

Oh, sorry, I misunderstood the first post.

Try this equation for the acceleration:

(g[-m1sin35°-m1cos35°μk+m2])/(m1+m2)

It gives 2,58 m/s^2

17. Mar 2, 2013

### SaxonMilton

Re: how to find acceleration given two masses , an angle ,and kinetic

18. Mar 2, 2013

### Bananas40

Re: how to find acceleration given two masses , an angle ,and kinetic

Did my equation work?

19. Mar 2, 2013

### lep11

20. Mar 2, 2013

### haruspex

Re: how to find acceleration given two masses , an angle ,and kinetic

I agree with that.