scrambler friction problems

[pineapple629]

we need to find the friction of our car after we launch it. it rolls to a stop at 10 meters.

http://home.comcast.net/~jay7042/physics.bmp

initial velocity after it laucnhed is 1.25 m/s
distance traveld 10m in 7s
we need to find the friction and efficiency of the car

[Chen]

Use energies. The only non-preserving force that operates in the system is the friction, and its work is equal to the change of mechanical energy of the whole system:
W_f = \Delta E_m = (\Delta E_k) + (\Delta E_p)
-fX = (0 - 0) + (0 - mgh) = -Mgh
Where M is the mass of the weight, and X is the total distance the car travels (1m + 10m), assuming there is also friction in the acceleration area (the 1m inside the structure). If there is no friction in that segment, then X is just 10m.

[pineapple629]

we are only going to calculate the 10m after it launched. i plugged my numbers into the bottom equation as best as i could and got -.023*10 = (-.178*9.8*1) = 1.97 now im confused what 1.97 is

[Chen]

Where did you come up with 0.023N as the friction force? I thought that's what you were going to find.
-fX = -Mgh
Therefore:
f = \frac{Mgh}{x} = \frac{2kg10\frac{m}{s^2}1m}{10m}