Find the average power of the crashed test car.

[pstrokeslibs]

Homework Statement

In a crash test, a test car of mass 1734 kg is moving at a speed of 30.9 m/s (= 69.5 miles per hour) when it crashes into a wall. If the car comes to rest in 0.8 s, how much average power (in W) is expended in this process?

Homework Equations

P=W/t to find "P"
W=Fd to find "W"
F=ma to find "F"
v=d/t to find "d"
a=v/t to find "a"

The Attempt at a Solution

i think the problem gives us, time(t)=0.8s, mass of car(m)=1734kg, velocity(v)=30.9m/s. i already did it by all of those equation, but the answer still wrong, or it's because of my equation that wrong.. sorry for my poor english, I am an Asian exchange student here in the US, please help me :(

thank you! :)

 

[rock.freak667]

Well the energy it has is kinetic energy, which is being used in the 0.8 seconds.

So use P = W/t and get the power.

 

[pstrokeslibs]

So we can use equation W=(delta)KE right? but what is the initial KE and final KE... I am sorry

should the initial velocity be 30.9m/s and the final velocity 0m/s?? I am going to use W=1/2m(finalvelocity^2-initialvelocity^2)

Thanks for help :D

 

[rock.freak667]

So we can use equation W=(delta)KE right? but what is the initial KE and final KE... I am sorry

should the initial velocity be 30.9m/s and the final velocity 0m/s?? I am going to use W=1/2m(finalvelocity^2-initialvelocity^2)

Thanks for help :D

Yes that would be it.

 

[pstrokeslibs]

i got it now! thanks very much! but... the 30.9 is final velocity...