Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    14
    ReputationRep:
    A guitar string has length 0.7m and cross sectional area o.2mm^2. A constant tension of 4.2N is applied to the string causing a strain of 0.015. Calculate the stress of the string.

    I got: F/A = 4.2/0.2*10-3 = 21000

    But the actual answer is 2.1* 10^7

    I really don't understand how they got that answer, can someone please explain it to me?
    Offline

    12
    ReputationRep:
    you haven't converted to meters properly

    work out what the radius is in mm, then convert to meters, then find the cross sectional area in meters squared.
    Offline

    9
    ReputationRep:
    You have to be careful when converting areas given in units other than square metres into square metres.

    For example, there are 100 cm in 1 m. Does this mean that there are 100 square cm in a square m? This cannot be right - you could arrange 100 squares, each of size 1 cm x 1 cm, along the edge of a metre ruler. But you would need 100 such rows to cover an area of one square metre (i.e. 1 m x 1 m), so that is 10,000 square cm in a square m!

    Can you see how to apply this idea in the case of your problem?
    Offline

    0
    ReputationRep:
    Have a think about what Pangol said first. Once you've made some progress, look at the way I've done it, using basic mathematical laws.

    Spoiler:
    Show
    1mm = 1m*10^-3

    square both sides

    1mm*1mm = 1m*1m*(10^-3)*(10^-3)

    1mm^2 = 10^-6*1m^2

    So you need to multiply by 10^-6 not 10^-3 to convert mm^2 into m^2
 
 
 
  • 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.

  • Poll
    What newspaper do you read/prefer?
  • 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.

  • 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

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