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

    14
    ReputationRep:
    Hi,

    Just wondering whether someone could help explain this to me. I have all the workings right for the question and my numerical answer agrees with what's in the back of my textbook but their written explanation differs from mine and I can't seem to make sense of theirs.

    The rest mass of an electron is 1.9 x10^-31 right?

    Both my answer and the back of the book agree that the increase in mass in this question is 1.956kg so I'm okay with that bit but it then goes on to say the following:

    The increase in mass is about twice the rest mass so the electron has three times greater mass than when at rest.

    Can anyone explain this to me?

    Thanks in advance,
    Blake
    Offline

    19
    ReputationRep:
    (Original post by Blake Jones)
    Hi,

    Just wondering whether someone could help explain this to me. I have all the workings right for the question and my numerical answer agrees with what's in the back of my textbook but their written explanation differs from mine and I can't seem to make sense of theirs.

    The rest mass of an electron is 1.9 x10^-31 right?

    Both my answer and the back of the book agree that the increase in mass in this question is 1.956kg so I'm okay with that bit but it then goes on to say the following:

    The increase in mass is about twice the rest mass so the electron has three times greater mass than when at rest.

    Can anyone explain this to me?

    Thanks in advance,
    Blake
    well if the rest mass is 1m
    and then that mass increases by 2m
    the final mass would be the rest mass plus the change in mass
    1m+2m=3m

    I guess that probably you were expecting to see a statement of what the mass increases to and this is throwing your brain off.
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by Joinedup)
    well if the rest mass is 1m
    and then that mass increases by 2m
    the final mass would be the rest mass plus the change in mass
    1m+2m=3m

    I guess that probably you were expecting to see a statement of what the mass increases to and this is throwing your brain off.
    but the increase in mass isn't twice the rest mass is it? Or am I reading the wrong numbers?
    Offline

    10
    ReputationRep:
    (Original post by Blake Jones)
    but the increase in mass isn't twice the rest mass is it?
    Yes. So what is the issue?

    Fractional increase in mass is

     \dfrac{m-m_0}{m_0} =\dfrac{3m_0 - m_0 }{m_0} = 2

    where  m_0 is rest mss of electron.

    The increase in mass is about twice the rest mass .....

    The new mass is  3m_0 which is three times greater than the rest mass,  m_0 .

    so the electron has three times greater mass than when at rest.
    Offline

    0
    ReputationRep:
    how did u guys do???
 
 
 
  • 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.