Turn on thread page Beta
    • Thread Starter

    Two particles P and Q have masses 3m and 5m respectively. They are connected by a ligth inextensible string which passes over a smooth light pulley fixed at the edge of a pulley. The coefficient of friction between P and the table is 0.6. The system is released from rest with the string taut. For the period before Q hits the floor or P reaches the pulley.

    a). Write down an equation of motion for each particle seperately

    b). Find, in terms of g, the accceleration of Q

    c). Find, in terms of m and g, the tension in the string

    When Q has moved a distance h, it hits the floor and the string becomes slack. Given that P remains on the table during the subsequent motion and does not reach the pulley.

    d). Find, in terms of h, the distance moved by P after the string becomes slack until P comes to rest.

    You have given no indication of what you have tried which is why you have had no answers, probably.

    Common errors here; students try to treat the system as if it were in equilibrium, which it isn't, both masses are accelerating. Another mistake is to stick N (for Newtons) all over the place in the equations so that it looks like there is a variable called N. Do not put units into equations.

    To start you off, for particle P, there is a tension in the string pulling it across the table and a Friction \mu R in the opposite direction.
    As the table is horizontal the reaction force R=3mg. These two forces combine to equal 3ma.

    Thus the equation of motion for P is
    T-\mu R=3ma\;\Rightarrow\;T-3\mu mg=3ma
    As the string is inextensible, the Tension at the other end of the string is the same (although in the opposite direction)

University open days

  • University of Exeter
    Undergraduate Open Days - Exeter Campus Undergraduate
    Wed, 24 Oct '18
  • University of Bradford
    Faculty of Health Studies Postgraduate
    Wed, 24 Oct '18
  • Northumbria University
    All faculties Undergraduate
    Wed, 24 Oct '18
Who do you think it's more helpful to talk about mental health with?
Help with your A-levels

All the essentials

The adventure begins mug

Student life: what to expect

What it's really like going to uni


Essay expert

Learn to write like a pro with our ultimate essay guide.

Uni match

Uni match

Our tool will help you find the perfect course for you

Study planner

Create a study plan

Get your head around what you need to do and when with the study planner tool.

Study planner

Resources by subject

Everything from mind maps to class notes.

Hands typing

Degrees without fees

Discover more about degree-level apprenticeships.

A student doing homework

Study tips from A* students

Students who got top grades in their A-levels share their secrets

Study help links and info

Can you help? Study help unanswered threadsRules and posting guidelines

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.