How Can I Calculate the Final Velocity of a Wagon on a Hill Using Physics?

[Izekid]

There's a wagon standing on a hill
The Height :0,81m
When v1 = 0m/s then v2 = 4m/s when the wagon has rolled down the slope.
What is the velocity when the startvelocity is 2m/s ...

How do I do this...

I've tried many things but I don't know the mass so how should I do?

Please help

 

[scimanyd]

try using potential and Kinetic energy equations

 

[Izekid]

Is this right?

Is this right then... I take 2m/s which is v1 and put in in kinetical energy equation and take out v^2= Sqrt 2*g*h = 4,45 which is the right answer but I don't seem right it must be harder than that

 

[scimanyd]

Energy is conserved;
Eintial = Efinal
Pei + Kei = Pef + Kef
mgh + 1/2mvi^2 = 1/2mvf^2

or from equations of motion:
v^2 = v0^2 + 2*a*x where x is h

both result in the same answer.