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Kinetic Energy watch

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    A particle of mass 5kg is moving at 2ms^-1 when it is acted on by a force of magnitude 10N for 2 seconds, causing it to accelerate. Find the increase in kinetic energy.

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    Before:

    KE=1/2 mv^2

    =5/2 x 4
    =10J

    After:

    F=ma
    10=5a
    a=2
    v=u+at
    v=2+4
    v=6

    KE= 5/2 x 36
    =90J

    Change in KE=90-10=80J

    EDIT: Opps... made mistake.

    Increase = 30J
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    (Original post by DOJO)
    A particle of mass 5kg is moving at 2ms^-1 when it is acted on by a force of magnitude 10N for 2 seconds, causing it to accelerate. Find the increase in kinetic energy.

    Thanks.
    Initial KE = (1/2)(5)(2)^2 = 20/2 = 10 J

    When acted on by force:
    -> F = ma
    -> 10 = 5a
    -> a = 2 ms^-2

    Hence: a = 2, t = 2, u = 2.
    -> v = u + at = 2 + (2 * 2) = 4 + 2 = 6 ms^-1

    Final KE = (1/2)(5)(6)^2 = 90 J

    Increase in KE = Final KE - Initial KE = 90 - 10 = 80 J
    • Thread Starter
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    (Original post by Nima)
    Initial KE = (1/2)(5)(2)^2 = 20/2 = 10 J

    When acted on by force:
    -> F = ma
    -> 10 = 5a
    -> a = 2 ms^-2

    Hence: a = 2, t = 2, u = 2.
    -> v = u + at = 2 + (2 * 2) = 4 + 2 = 6 ms^-1

    Final KE = (1/2)(5)(6)^2 = 90 J

    Increase in KE = Final KE - Initial KE = 90 - 10 = 80 J
    Cheers,

    I would give both of you a postive rep but unfortunantly this thing is not
    letting me!
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    (Original post by Nima)
    When it lets you rep, give it to me, because the 1st poster was wrong in his/her answer.
    Harsh :rolleyes: Its not been a good day for me, I keep making silly mistakes, but give Nima the rep
 
 
 
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