Three Pulleys 3 masses, find tension

  • Thread starter Thread starter Purple Grind
  • Start date Start date
  • Tags Tags
    Pulleys Tension
AI Thread Summary
The discussion revolves around calculating the tension in a system of three masses (m1 = 6 kg, m2 = 2 kg, m3 = 3 kg) suspended from massless, frictionless pulleys. The user attempts to derive the tension using equations of motion but consistently arrives at 15.68 N, which does not match any provided answer choices. Other participants confirm the user's equations are correct but suggest a misinterpretation of the problem. The conversation highlights the importance of careful reading and verification in solving physics problems. Ultimately, the tension is noted to be around 16 N, indicating a possible error in the answer options provided.
Purple Grind
Messages
3
Reaction score
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?
 
Physics news on Phys.org
Your equations are right but your answer is wrong. Please post your working.
 
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
 
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.
 
k thanks
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...

Similar threads

Back
Top