Am I on the right track?

Question:
A. A car that weighs 12000.0 N is initially moving at a speed of 57.0 km/hr when the brakes are applied and the car is brought to a stop in 2.6 s. Find the magnitude of the force that stops the car, assuming it is constant.

B. What distance does the car move during this time?

Okay so I drew the diagram and I am planning on using the f=ma equation but I think I need to solve for a first using Vf=Vo + at. Am I on the right track or am I completely off??
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 Recognitions: Homework Help Yes, you're on the right track.
 Okay so I did... (57 km/hr)^2 = a x (2.6s) and I got 1249.6 m/s^2...which way wrong...where am I going wrong?

Am I on the right track?

Wait I wrote that backwards sorry...

I got...

0 = (57 km/hr)^2 +a(2.6s)

Recognitions:
Homework Help
 Quote by BuBbLeS01 Wait I wrote that backwards sorry... I got... 0 = (57 km/hr)^2 +a(2.6s)
Why are you squaring 57?
 Recognitions: Gold Member Homework Help Science Advisor Why are you squaring the velocity? And you've got to be consistent with your units...you can't have seconds on one side of the equation and hours on the other without introducing a conversion factor.
 oh my gosh I don't know why I am squaring it...I am looking at the wrong equation. Okay I changed 57 km/hr to 0.01583 km/s. Now I have... 0 = 0.01583 km/s + a (2.6s)... (-0.01583 km/s) / (2.6s) = a so now I can use f=ma f= (12000.0 N) x (0.0060897 km/s^2)

Recognitions:
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 Quote by BuBbLeS01 oh my gosh I don't know why I am squaring it...I am looking at the wrong equation. Okay I changed 57 km/hr to 0.01583 km/s. Now I have... 0 = 0.01583 km/s + a (2.6s)... (-0.01583 km/s) / (2.6s) = a so now I can use f=ma f= (12000.0 N) x (0.0060897 km/s^2)
careful... you should use m/s for velocity and m/s^2 for acceleration (because your force equation requires kg for mass and m/s^2 for acceleration... to get the result in N)...

and also 12000.0N isn't the mass, it's the weight... get the mass of the object.

 Quote by learningphysics careful... you should use m/s for velocity and m/s^2 for acceleration (because your force equation requires kg for mass and m/s^2 for acceleration... to get the result in N)... and also 12000.0N isn't the mass, it's the weight... get the mass of the object.
okay so this is what I have now...

0=15.83 m/s + a x (2.6s)
(-15.83m/s) / (2.6s) = a = (-6.08846)

w=mg
12000/9.8=1224.49

f=ma
1224.49 * -6.08846 = -7455.26 N
That is really big!!

Recognitions:
Homework Help
 Quote by BuBbLeS01 okay so this is what I have now... 0=15.83 m/s + a x (2.6s) (-15.83m/s) / (2.6s) = a = (-6.08846) w=mg 12000/9.8=1224.49 f=ma 1224.49 * -6.08846 = -7455.26 N That is really big!!
Looks good. That's the right answer.

 Quote by learningphysics Looks good. That's the right answer.
It says its incorrect....I don't know what is wrong.

Recognitions:
Homework Help
 Quote by BuBbLeS01 It says its incorrect....I don't know what is wrong.
I don't think you carried enough decimal places... I get -7456.8N

 Quote by learningphysics I don't think you carried enough decimal places... I get -7456.8N
should I be entering it as positive since its the magnitude?

Recognitions:
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 Quote by BuBbLeS01 should I be entering it as positive since its the magnitude?
Yes! I didn't notice that it asked for magnitude!

 Quote by learningphysics Yes! I didn't notice that it asked for magnitude!
Yay it's right!! Hehe...Thank you so much for your time!! I really do appreciate it!!

Recognitions:
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 Quote by BuBbLeS01 Yay it's right!! Hehe...Thank you so much for your time!! I really do appreciate it!!
no prob.
 How do I start the second part of this question?