Turn on thread page Beta

    (Original post by shift3)
    Gaz, can you do question 35? (review ex p157)
    As the rail is smooth the reaction acts only perpendicular to the point of contact.
    Let the reaction at the rail be S and the reaction at the ground be R and F.
    Let the angle of elevation be t.
    As the reaction is pependicular to the slope it acts at an angle (90-t) to the horizontal.

    Resolving vertically: Ssin(90-t) + R = 20g
    Scost + R = 20g

    Resolving horizontally: Scos(90-t) = F
    Ssint = F

    Taking moments about A:
    C = AC
    (20g)(3cost) = (Scost)(5cost) + (Ssint)(5sint)
    60gcost = 5S(sin^2 t + cos^2 t)
    S = 60gcost/5

    Using trigonometry. sint = 3/5. Hence cost = 4/5
    Substituting gives S = 94N(nearest N)

    (b) F = uR
    u = F/R = (Ssint)/(20g-Scost) [From earlier resolving force equations]
    Substituting exact values gives 0.47 (2dp)

    (c) R = 20g-Scost = 120.736
    F = Ssint = 56.448

    Magnitude = rt[120.736^2 + 56.448^2] = 133N (nearest N)

    Feel free to ask if there's anything else i can help with.
    • Thread Starter

    Oh.. The reaction of the rail was directed towards the rod, not to the ground.

    Thanks Gaz!
Turn on thread page Beta
Updated: January 21, 2005

University open days

  • Heriot-Watt University
    School of Textiles and Design Undergraduate
    Fri, 16 Nov '18
  • University of Roehampton
    All departments Undergraduate
    Sat, 17 Nov '18
  • Edge Hill University
    Faculty of Health and Social Care Undergraduate
    Sat, 17 Nov '18
Have you ever experienced bullying?
Useful resources

Make your revision easier


Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here


How to use LaTex

Writing equations the easy way


Best calculators for A level Maths

Tips on which model to get

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.