Simple moments q. with diagram Watch

biatch
Badges: 0
Rep:
?
#1
Report Thread starter 9 years ago
#1
Heinemann Edexcel- Review exercise 2 q. 35.

The diagram shows a uniform solid hemisphere of mass m, base radius a and with centre of mass G. The hemishere is freely pivoted at a point A on the circumference of it's plane face and a light string connects B to a point C on the horizontal plane through A. The system is in equilibrium with A, B, C and G in the same vertical plane, BC is perpendicular to AB and AB is inclined to AC at an angle  θ where tan  θ = 4/3. Show that the thrust in the spring has magnitude 3mg/20.

Here's what I've done so far: I took moments from A, perpendicular to the plane =>
mga cos  θ = 2aT
cos  θ = 3/5  ∴ 3mga/5 = 2aT
T = 3mg/10

Where have I gone wrong? Thanks in advance.
Attached files
0
quote
reply
biatch
Badges: 0
Rep:
?
#2
Report Thread starter 9 years ago
#2
please help, this is driving me nuts!! :eek3:
0
quote
reply
ghostwalker
  • Study Helper
Badges: 15
#3
Report 9 years ago
#3
Please draw the diagram, with the points labelled, and the spring shown. As it stands, I can't make any sense of it.
quote
reply
biatch
Badges: 0
Rep:
?
#4
Report Thread starter 9 years ago
#4
ok, here's the revised diagram.
Attached files
0
quote
reply
ghostwalker
  • Study Helper
Badges: 15
#5
Report 9 years ago
#5
I think you are making the mistake of assuming that the centre of mass of the solid hemisphere is in the middle of the flat face.
quote
reply
biatch
Badges: 0
Rep:
?
#6
Report Thread starter 9 years ago
#6
Right, now I see. I was trying to 'turn' the action of the mass by using the cosine function, which I now know is wrong. Thanks
0
quote
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
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

University open days

  • University of Buckingham
    Psychology Taster Tutorial Undergraduate
    Fri, 14 Dec '18
  • University of Lincoln
    Mini Open Day at the Brayford Campus Undergraduate
    Wed, 19 Dec '18
  • University of East Anglia
    UEA Mini Open Day Undergraduate
    Fri, 4 Jan '19

Were you ever put in isolation at school?

Yes (90)
25.86%
No (258)
74.14%

Watched Threads

View All
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