Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Work and Energy Problems [help]

  1. May 16, 2004 #1
    1) How much work does it take to accelerate an electron(mass=9.11x10^-31kg)
    from rest to a speed of 5.0x10^6 ms?

    I know you have to use more than 1 equation to solve it but I can't seem to get close to an answer.

    2) How much work must be done to stop a 1000-kg car travelling at 100km/h?

    Is it me or does this question not have enough info.
     
  2. jcsd
  3. May 16, 2004 #2

    Doc Al

    User Avatar

    Staff: Mentor

    It's you. :smile: Remember that work done on an object equals its change in KE.
     
  4. May 16, 2004 #3
    KE = 1/2mv^2
    KE = 1/2(1000)(27.278)^2
    KE = 385809 Joules
    So the work to stop it would be that much?
     
  5. May 16, 2004 #4
    And I assume the 1st question is done the same way?
     
  6. May 16, 2004 #5

    Doc Al

    User Avatar

    Staff: Mentor

    That's the idea. (Check your conversion of 100km/hour.) (Don't state so many significant figures in your answer.)

    And, yes, the first problem is the same idea.
     
  7. May 16, 2004 #6
    Thanks SOO MUCH!
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook