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What is the tension in string?

  • #1

Homework Statement


We have to find T1 and T2
upload_2018-6-29_12-48-6.png

From right to left objects are: A B C

Homework Equations


F=ma

The Attempt at a Solution


Okay. So I found acceleration of whole system:
F=ma
200N= (20+10+5)*a
200/35=a
a= 40/7 ms-2

Now, finding T1 is fairly simple:
f=ma
T1=5*(40/7)
T1=200/7 Newtons (Let's not reduce it right now to decimals)


Now, T2. This is where the problem arises.
T2 can be calculated by the difference of the forces on object A.
f=ma
Force on A= 10kg*(40/7)
= 400/7 Newtons

T2 will be:
200-T2= 400/7
200-400/7= T2
1000/7 Newtons= T2

1000/7N= 142.75 Newtons.



Is this answer correct? Please tell me. I'm very confused.
Thank you for reading.
 

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Answers and Replies

  • #2
Orodruin
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It is not clear from your description what A is, bit it seems to be the 10 kg mass to the right by your attempt.

200= T2- 400/7 (T2 is greater than 400/7 N but obviously lesser than 200 N)
200-400/7= T2
Apart from the fact that you made a sign error in the first that mysteriously disappeared in the second step, yes, this is a viable approach.
 
  • #3
It is not clear from your description what A is, bit it seems to be the 10 kg mass to the right by your attempt.


Apart from the fact that you made a sign error in the first that mysteriously disappeared in the second step, yes, this is a viable approach.
Thanks a bunch for:
a) Replying and conforming
b) pointing out the mistakes in the query.
I have corrected them.
 
  • #4
CWatters
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Your method for T2 works but why not just erase mass A and the 200N force and apply f=ma to what's left.
 

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