1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

A Car with Constant Power

  1. Mar 17, 2009 #1
    1. The problem statement, all variables and given/known data
    The engine in an imaginary sports car can provide constant power to the wheels over a range of speeds from 0 to 70 miles per hour (mph). At full power, the car can accelerate from zero to 30.0 mph in time 1.30s .

    At full power, how long would it take for the car to accelerate from 0 to 60.0 mph ? Neglect friction and air resistance.

    2. Relevant equations

    No clue

    3. The attempt at a solution
    I assumed that since it takes 1.3s to go from 0-30, it would take 2.6 to got from 0-60, yet it was wrong and got this for a feedback. :
    Think about how kinetic energy is related to velocity, and how power is related to energy.
     
  2. jcsd
  3. Mar 17, 2009 #2
    The feedback you got should give you a clue as to what the relevant equations are. Do you know of some equations which relate kinetic energy to velocity and power to energy?
     
  4. Mar 17, 2009 #3
    KE=1/2mv^2 and Power=??
     
  5. Mar 17, 2009 #4

    LowlyPion

    User Avatar
    Homework Helper

    Welcome to PF.

    Constant power is constant watts.

    What is a watt? J/s

    What is a joule?

    well ... it's the units of ½mv² for one thing.
     
  6. Mar 18, 2009 #5
    power = force(instantenuous) X speed (instantenuous)
     
  7. Mar 18, 2009 #6
    Im still stumped! I have no clue how to transfer from knowing 1.3s at Full power to go from 0-60
     
  8. Mar 18, 2009 #7
    I would figure out the acceleration of the car first using the 0-30 in 1.3 sec. then use the known acceleration (since it would be constant at full power) to find out how long it would take the car to go 0-60 with that acceleration.
     
  9. Mar 19, 2009 #8

    LowlyPion

    User Avatar
    Homework Helper

    Think of power then as something that is added at a constant rate. It's energy after all and as it collects it becomes kinetic energy of your car.

    If it took one bucket of energy to get you to 1/2mv2 then how many buckets of energy will it take to get you to 1/2m(2v)2 ?

    Since the buckets are added in this case at 1.3s per bucket - a constant rate -...
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: A Car with Constant Power
  1. Constant Power (Replies: 11)

  2. Constant Power (Replies: 6)

Loading...