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: Life in the Fast Lane

  1. Nov 8, 2004 #1
    Hello Everyone. I am almost through my on-line coarse on Introductory Physics. I am taking my last self-assessment before the on-line certification in two weeks. There is just one problem that has my confused. Please provide some guidance. Thanks.

    Accelerating Car - What is the average power required to accelerate a 1200 kg car from rest to a velocity of 20 m/s in 10 seconds?

    I am not even sure exactly where to start. I know that power can be measured in joules/sec a metric unit known as a watt. I do know some related formulas that might apply. They include:

    Power = Change in Energy/Change in time
    F = ma
    W = Fd

    I am still unclear how to proceed to determine that answer to this question in watts. :eek:
  2. jcsd
  3. Nov 8, 2004 #2


    User Avatar
    Science Advisor
    Homework Helper

    You have another:
  4. Nov 8, 2004 #3
    How appropriate. If anyone can help me it is the master of falling (accelerating) bodies...Galileo. Anyway, I am still confused on why your formula is the one I should start with. Can you explain? If I do use this formula I get:


    Now, is this watts? Also, is it important to consider the 10 second time in calculating the avergae power? If so then maybe the answer should be 240,000/10=24,000 watts. What do you think? I am on tract? Thanks.
  5. Nov 8, 2004 #4


    User Avatar
    Science Advisor
    Homework Helper

    Looks good to me :approve:

    The car is started at rest, so it had no kinetic energy.
    After 10 seconds it had 240,000 J of kinetic energy.

    So it gained 24.000 J per second on average.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook