I'm trying to calulate the efficency of a small hydrogen fuell cell that I built. I have all of the measurements, but I'm not coming up with a resonable effiency. The power to electrolyze the water is the P IN. 3.25 W =2.5 V x 1.3Amps (.21 mA) We measured the electrical power out finding the voltage and amperage. P OUT = V x I 2.01 x 10^-4 W=.96 V x .00021 AMPS (.21 mA) I caulcate the force to be 1.421 N Then I take the electrical P Out and use it as the P IN for the car the P IN for the car is the electrical P Out and the P Out for the car is F x V To find the % efficiency: The avg velocity is .0198 m/s For the car: (there is something wrong here since I'm getting more power out) P in = 2.01 x 10^-4 W P Out = F x V 2.81 x 10^-2 J = 1.421 N x .0198 m/s I'm coming up with an unreasonable calculation Isn't watts joules per second. Should I be including the time it took to electrolyze the water. I'm just using the formula i was given, but the units don't work out Also I'm not sure if i'm calculating the force in th right way. We used a spring scale and my measurement was .160 kg. I'm I just supposed to multiply that by 9.8 m/s^2. I know that this way gives me Newtons, but the car isn't being affected by gravity anyways. If someone could look this over I'd appreciate it.