Three Pulleys 3 masses, find tension

In summary, the tension of the strings in a system with three objects suspended from three massless and frictionless pulleys, with masses of 6 kg, 2 kg, and 3 kg, respectively, and set in motion, is approximately 15.68 N. This is calculated using the equations a1=(m1g-T)/m1, a2=(2T-m2g)/m2, a3=(m3g-T)/m3, and 2a2=a1+a3, with a resulting value of T=15.68.
  • #1
Purple Grind
3
0

Homework Statement



Three objects mI. m2 and m3 are suspended
from three massless and frictionless pulleys as
shown in the diagram. ml is 6 kg, m2 is 2 kg
and m3 is 3 kg. Find the tension of the string
when the system is set in motion (i.e. all
masses are moving). Answer in N

Options are:
(a) 11.3 (b) 12.1 (c) 13.5 (d) 14.2

..O...O... Top 2 pulleys attached to ceiling, m1 hangs from 1st pulley, m2 is attached
.| |..| |... to the middle pulley, m3 hangs from third pulley.
.|..O...|
.|..[]..|
[] m2 []
m1...m3

Homework Equations


Fg=mg
F=ma

The Attempt at a Solution



I made 3 equations, tried to relate them but I am getting 15.68N instead of any of the options (this was an old exam question). It's too far from 14.2 to be right. Here were the four equations I made:

a1=(m1g-T)/m1
a2=(2T-m2g)/m2
a3=(m3g-T)/m3

2a2=a1+a3

I keep getting none of the possible answers but I think I'm doing it right. Where did I go wrong?
 
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  • #2
Your equations are right but your answer is wrong. Please post your working.
 
  • #3
a1=(m1g-T)/m1=g-T/m1=g-T/3
a2=(2T-m2g)/m2=2T/m2-g=T-g
a3=(m3g-T)/m3=g-T/m3=g-T/6


From 4th eqn:

2T-2g=g-T/3+g-T/6

2T+T/2=4g

5T/2=4(9.8)

T=15.68
 
  • #4
Oh, sorry, I misread the end of your first post. I thought you were getting 14.2. So, I agree with you, it's something around 16.
 
  • #5
k thanks
 

Related to Three Pulleys 3 masses, find tension

1. What is the setup for a three pulley system with three masses?

A three pulley system with three masses consists of three separate masses connected by strings or ropes and wrapped around three different pulleys. The masses are usually labeled as m1, m2, and m3 and the strings are assumed to be massless and frictionless.

2. How do you calculate the tension in the strings in a three pulley system with three masses?

To calculate the tension in the strings, you will need to use Newton's Second Law, which states that the sum of the forces acting on an object is equal to the mass of the object multiplied by its acceleration. By using this law and considering the forces acting on each mass, you can solve for the tension in each string.

3. What are the factors that affect the tension in a three pulley system with three masses?

The tension in a three pulley system with three masses is affected by the masses of the objects, the angles at which the strings are pulled, and the force of gravity. The tension in each string will be different depending on these factors.

4. How does the number of pulleys affect the tension in a three pulley system with three masses?

The number of pulleys does not affect the tension in a three pulley system with three masses. As long as the strings are all connected and wrapped around the pulleys in the same way, the tension will remain the same.

5. Can you determine the tension in a three pulley system with three masses without knowing the masses or angles?

No, in order to calculate the tension in a three pulley system with three masses, you will need to know the masses of the objects and the angles at which the strings are pulled. Without this information, it is not possible to determine the tension in the strings.

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