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Homework Help: Finding units for power via Dimensional Analysis? Makes no sense

  1. Jul 30, 2011 #1
    1. The problem statement, all variables and given/known data

    "Power is the rate at which work is performed.

    Power is signified by W for watts.

    Power is also the amount of energy transmitted in a unit of time (s).

    Energy is measured in joules. Joules have the units of Newton∙meters.

    A Newton is a unit of force. It is equal to the amount of force required to give a 1 kilogram mass and acceleration of one meter per second squared."

    Using the aforementioned information, determine the units for power by completing a dimensional analysis.

    2. Relevant equations

    3. The attempt at a solution

    Ok so I know that the units for power are Joules/seconds.. How would you go about getting this by dimensional analysis at all?

    So I've done

    P = J/s

    Power (P) = Work (W)/time (t)
    P is in Watts (W)
    Watts is J/s

    Not sure at all what to do, this is worded so weirdly.. If anyone could help me see what exactly to do, that'd be appreciated.
  2. jcsd
  3. Jul 30, 2011 #2
    Currently, you have done this question by working backwards. You were pretty much there.

    The unit for Force is Newtons

    Work = force * distance. Hence, the units for work is Newtons * distance (Nm) which is equivalent to Joules.

    Now, reapply this to what you've already done and you're pretty much there.
  4. Jul 30, 2011 #3
    It might be asking you to get strictly down to units of kg, m, and s.
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