Turn on thread page Beta
    • Thread Starter
    Offline

    10
    ReputationRep:
    You are given a diagram which shows a toy consisting of a light plastic aeroplane suspended from a long spring.

    First you're asked to draw a displacement against time graph which I did.

    Its the next bit that confuses me;

    "The aeroplane is replaced by a heavier model made of the same plastic having the same fuselage but larger wings. State and explain TWO changes which this substitution will make to the displacement against time graph that you have drawn for part i."

    I know the the amplitude will decrease for a larger mass but Im not sure the reason WHY. And also, Im not too sure about the second reason - the markscheme says the frequency will decrease as acceleration decreases. They use a=(2pi*f)^2 * x but I know that a is proportional to x so as far as i can see x will also decrease - so why would the frequency decrease? Please could someone explain - much appreciated thank you
    Offline

    10
    ReputationRep:
    Don't you have to think about how (ang) freq is related to mass? Like this http://ncalculators.com/images/formu...-frequency.jpg

    And the larger wings will produce a larger resistive force so cause damping?

    That would be my two guesses - but I can't see the picture.
    Offline

    20
    ReputationRep:
    (Original post by MrToodles4)
    You are given a diagram which shows a toy consisting of a light plastic aeroplane suspended from a long spring.

    First you're asked to draw a displacement against time graph which I did.

    Its the next bit that confuses me;

    "The aeroplane is replaced by a heavier model made of the same plastic having the same fuselage but larger wings. State and explain TWO changes which this substitution will make to the displacement against time graph that you have drawn for part i."

    I know the the amplitude will decrease for a larger mass but Im not sure the reason WHY. And also, Im not too sure about the second reason - the markscheme says the frequency will decrease as acceleration decreases. They use a=(2pi*f)^2 * x but I know that a is proportional to x so as far as i can see x will also decrease - so why would the frequency decrease? Please could someone explain - much appreciated thank you
    for the same spring...
    frequency decreases (period increases) when mass increases
    T=2π sqrt(m/k)

    probably they're hoping you'll say something about damping for the larger wings.
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by phys981)
    Don't you have to think about how (ang) freq is related to mass? Like this http://ncalculators.com/images/formu...-frequency.jpg

    And the larger wings will produce a larger resistive force so cause damping?

    That would be my two guesses - but I can't see the picture.
    That makes sense thank you so much. And I do not have that equation for my OCR spec - so Im just wondering how is it exactly that frequency is related to that equation - so as mass increases frequency decreases? Is that always the case? thanks again
    Offline

    10
    ReputationRep:
    (Original post by MrToodles4)
    That makes sense thank you so much. And I do not have that equation for my OCR spec - so Im just wondering how is it exactly that frequency is related to that equation - so as mass increases frequency decreases? Is that always the case? thanks again
    yes, that should always be the case.

    The other response above mentions the equaiton in a different form, to find period T rather than frequency but they're different forms of the same equation. I'd be surprised if you didn't need this in some form for OCR (but I don't know much about OCR).

    Edited to add - a quick look at OCR spec and you're right, I can't see this, which explains I suppose why the MS expresses it in the form it does. . It can be derived however if you have done shm and if you've done Force and spring constants (F = kx) elsewhere, so is worth knowing.
    Offline

    20
    ReputationRep:
    Fwiw this is what you get on the AQA datasheet

    Name:  oscillations aqa datasheet.JPG
Views: 25
Size:  24.8 KB
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by phys981)
    yes, that should always be the case.

    The other response above mentions the equaiton in a different form, to find period T rather than frequency but they're different forms of the same equation. I'd be surprised if you didn't need this in some form for OCR (but I don't know much about OCR).

    Edited to add - a quick look at OCR spec and you're right, I can't see this, which explains I suppose why the MS expresses it in the form it does. . It can be derived however if you have done shm and if you've done Force and spring constants (F = kx) elsewhere, so is worth knowing.
    alright ill just try and remember the form of equation you've given me. Thank you so much again
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by Joinedup)
    Fwiw this is what you get on the AQA datasheet

    Name:  oscillations aqa datasheet.JPG
Views: 25
Size:  24.8 KB
    Thank youuuu
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: February 17, 2018
The home of Results and Clearing

2,832

people online now

1,567,000

students helped last year

University open days

  1. London Metropolitan University
    Undergraduate Open Day Undergraduate
    Sat, 18 Aug '18
  2. Edge Hill University
    All Faculties Undergraduate
    Sat, 18 Aug '18
  3. Bournemouth University
    Clearing Open Day Undergraduate
    Sat, 18 Aug '18
Poll
A-level students - how do you feel about your results?

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