Power Calc: Net vs Driving Force

[Janiceleong26]

Homework Statement

P=Fv,
I am confuse with which force to substitute into the equation. Is it the net force? or the driving force? (if it is a car) ..

 

[haruspex]

Homework Statement

P=Fv,
I am confuse with which force to substitute into the equation. Is it the net force? or the driving force? (if it is a car) ..

It depends on what power is to be determined, but whichever force you pick it must be a velocity that the force travels at.
E.g. a cyclist pushes with a force F_p on a pedal, and the pedal moves at tangential velocity v_p. The power delivered by the foot is P_p=F_pv_p. The frictional force between the rear tyre and the road is F_r. The bicycle advances at roadspeed v_r. The power the tyre/road produces is P_r=F_rv_r. Because of losses, P_r<P_p.

 

[Janiceleong26]

It depends on what power is to be determined, but whichever force you pick it must be a velocity that the force travels at.
E.g. a cyclist pushes with a force F_p on a pedal, and the pedal moves at tangential velocity v_p. The power delivered by the foot is P_p=F_pv_p. The frictional force between the rear tyre and the road is F_r. The bicycle advances at roadspeed v_r. The power the tyre/road produces is P_r=F_rv_r. Because of losses, P_r<P_p.

Thanks! I got it now