# Homework Help: Power and rate of potential energy

1. Dec 20, 2011

1. The problem statement, all variables and given/known data
A train of mass 2.0*10^5 kg moves at a constant speed of 72km/h up a straight incline against a frictional force of 1.28*10^4N.The incline is such that the train raises vertically 1m for every 100m travelled along the incline.
(i)Calculate the rate of increase per second of the potential energy of the train.
(ii) THe necessary power developed by train.

2. Relevant equations
P.E=mgh
P=W/t
=Fv

3. The attempt at a solution
Heres how i tried to solve it..
(i)convert 72km/h to m/s we get 20m/s
for 1 second, the train travels 20m
To find height when train travelled 20m,
sin^-1(1/100)=0.573 degrees
sin0.573=x/20
x=0.2m
so,

P=mgh/t
=(2x10^5)(10)(.2)/1s
=400kW

(ii)P=Fv
Since there is constant velocity, F-1.28*10^4=0
F=above N
P=Fv
=(1.28*10^4)(20)
=256kW

is this correct?

2. Dec 20, 2011

### LawrenceC

What about power needed to move train?

3. Dec 20, 2011

oh wait, so the total power needed by the train is just adding up the two anwsers above?

4. Dec 20, 2011

### LawrenceC

Yes.

5. Dec 20, 2011