Power of a biker riding downhill

[rainman123]

A biker rides on a motorcycle down the hill, and the motocycle exerts a force of F1 down the hill. The motorcycle also has mass, and therefore there is a gravitational force F2 acting on the motorcycle down the mill. The bike travels a distance D1 down the hill. It took the motorcycle time T1 to do so.

 

What is the power required by the motorcycle to perform this?

 

Is the power consmed by the motorcycle: Power1=(F1*D1)/T1

,or is the power consumed: Power2=((F1+F2)*D1)/T1

 

 

I guess my question is, Net Power is not the same as the power consumed by the motorcycle motor right, because net power is Power2 but the motorcycle motor provides only Power1, right

[John Cuthber]

He's going down hill. Even with the engine switched off he would still roll down the hill and accelerate until the wind resistance (etc) was dissipating energy as fast as gravity was providing it.

The engine isn't the only power source here.

[rainman123]

I know that. Thats what I am asking. If the motorbike is going down hill. Gravity gives it a component of force going downhill. The motorbike engine also gives it a force component down hill.

 

Then if I were interested in the amount of power that the motorcycle engine had to have consumed doing this task, how do I figure out the power?

 

Is the power consumed by engine P=F1*D1/T1?

 

But the total force of the system is F1+F2=F_total

 

so is it wrong for someone to calculate total power = F_total*D1/T1? This is because we want to know the power used by the engine, not the total power of engine and gravity put together. Right?

[swansont]

The work done by the engine is whatever KE you have at the bottom in excess of mgh, which will also be the force exerted by the motorcycle multiplied by the distance.

[cameron marical]

f1=3mph power1=(3mph*20m)/10 min so power1=6something.

f2=4mph power2=(3mph+4mph)*20min/10min so power2=14something

d1=20m

t1=10min