moz4rt
Badges: 10
Rep:
?
#1
Report Thread starter 2 years ago
#1
Image
https://gyazo.com/511685f0a4f7e44488188d6121d3a115

I tried equating the weight of the uniform rod to the to the vertical component of the tension in the string as well as using moments about point P, what else should I try?
0
reply
ghostwalker
  • Study Helper
Badges: 17
#2
Report 2 years ago
#2
(Original post by moz4rt)

I tried equating the weight of the uniform rod to the to the vertical component of the tension in the string as well as using moments about point P, what else should I try?
Moments about P would do it. Post working if it's not coming out.

Resolving vertically won't work, since you don't know the vertical reaction at P.
0
reply
Faction Paradox
Badges: 13
Rep:
?
#3
Report 2 years ago
#3
(Original post by moz4rt)
Image
https://gyazo.com/511685f0a4f7e44488188d6121d3a115

I tried equating the weight of the uniform rod to the to the vertical component of the tension in the string as well as using moments about point P, what else should I try?
Moments about point P are going to be the way to go, as the is a force upwards at P, so equating the weight is not going to give you the actual vertical force at Q.
0
reply
Nagromicous
Badges: 9
Rep:
?
#4
Report 2 years ago
#4
(Original post by Faction Paradox)
Moments about point P are going to be the way to go, as the is a force upwards at P, so equating the weight is not going to give you the actual vertical force at Q.
Do you have the correct answer? I got that T = 2g, but I won't bother explaining if it's incorrect.
Edit: I also got that the natural length = 75/31 = 2.419m.
0
reply
moz4rt
Badges: 10
Rep:
?
#5
Report Thread starter 2 years ago
#5
I got the correct answer this time, but instead of using the distance from P to Q I used the distance from P to R, can someone explain why this worked?
0
reply
moz4rt
Badges: 10
Rep:
?
#6
Report Thread starter 2 years ago
#6
Nevermind haha, for some reason I was using the distance on the line PR rather than using the line PQ, thanks!
0
reply
moz4rt
Badges: 10
Rep:
?
#7
Report Thread starter 2 years ago
#7
Also, why is there a reaction force at the hinge, but not the fixed point?
0
reply
Faction Paradox
Badges: 13
Rep:
?
#8
Report 2 years ago
#8
(Original post by moz4rt)
Nevermind haha, for some reason I was using the distance on the line PR rather than using the line PQ, thanks!
Haha yeah I do that kind of things loads in mechanics, quite often I don't read the questions fully and try and answer an entirely different question
0
reply
Nagromicous
Badges: 9
Rep:
?
#9
Report 2 years ago
#9
(Original post by moz4rt)
I got the correct answer this time, but instead of using the distance from P to Q I used the distance from P to R, can someone explain why this worked?
Was the answer I said correct?
0
reply
moz4rt
Badges: 10
Rep:
?
#10
Report Thread starter 2 years ago
#10
(Original post by Nagromicous)
Was the answer I said correct?
No, it was 3g/2, what did you do?
0
reply
Faction Paradox
Badges: 13
Rep:
?
#11
Report 2 years ago
#11
(Original post by moz4rt)
Also, why is there a reaction force at the hinge, but not the fixed point?
When you are considering moments about P, you are purely considering the forces on PQ, so in this consideration of moments it doesn't factor it.

But there is a reaction force at R, it has the same magnitude as the tension and acts in the opposite direction, as otherwise the system wouldn't be in equilibrium.
0
reply
Nagromicous
Badges: 9
Rep:
?
#12
Report 2 years ago
#12
(Original post by moz4rt)
No, it was 3g/2, what did you do?
I took moments about P but erroneously used the value for sin(a) when I meant to use the value for cos(a). I wrote down cos(a) but copied the wrong number. :/

5g x (3/2) x cos(a) = 3T
4.5g = 3T
T = 1.5g
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Have you experienced financial difficulties as a student due to Covid-19?

Yes, I have really struggled financially (77)
18.03%
I have experienced some financial difficulties (123)
28.81%
I haven't experienced any financial difficulties and things have stayed the same (160)
37.47%
I have had better financial opportunities as a result of the pandemic (54)
12.65%
I've had another experience (let us know in the thread!) (13)
3.04%

Watched Threads

View All