## A constant power is supplied to an Electric train?

Question by Red Jacket: A constant power is supplied to an Electric train?
The following is a question from the Indian Regional Physics Olympiad.

Assume that a constant power P is supplied to an electric train and is fully used in accelerating the train.Obtain relations giving the velocity of the train and distance traveled by it as functions of time.

Please show detailed working.Thanks.

Energy supplied is P* t ( at any time t)
E=Pt=Kinetic energy of train
0.5 m v2= Pt
v2= 2P/m * t
v= k * t^0.5 (k- constant)

dx/dt = k * t^ 0.5

Get x as a function of t.
Rearrange above to get t as function of x and substitute in velocity equation.

## electric trains are often supplied with 750V or even 30000V. Why do they use such high voltages?

Question by Max Tate: electric trains are often supplied with 750V or even 30000V. Why do they use such high voltages?
for physics hwk ðŸ˜€ oh and can u plz try and answer this too?? In the US homes are supplied with 120V, but in UK, 230V, what is disadvantage with US voltage?? THANKS xDD

Answer by Must Know Everything
High voltage means low current for the same power. Lower current means less losses in the transmission lines. I am drunk (listening to Led Zepplin very loud) but I think I am right…..