Energy Methods
kinetic energy 
E_{kinetic} = ½mv² 
m = mass, v = velocity 
(gravitational) potential energy (change) 
E_{gravitational} = mgΔh  m = mass, h = height (change), g = gravitational field strength (= 9.8 N/kg) 
elastic (potential) energy 
λ = modulus of elasticity, l = unstretched length, x = extension (= current length  l ) 

work done against a force (often resistive or frictional, but not always) 
E_{work} = Fs E_{work}(= F.s = Fs cosθ) 
F = force, s = distance moved, using the component along the line of the force. The the vector formulation is not often needed. 
power 
E can stand for any form of energy 

power  P = F v 
F = force, P = power, v = velocity 
ΔKE + ΔGPE + Δwork = 0  The signs are all positive at this stage because this is just the standard equation 
(½mv²  2.5m)  1960 m + 490 m = 0 
Signs have become negative where our logic has told us that the value we are substituting is negative 
½v² = 1472.5 
Cancelling by m and rearranging 
v = 54 m/s 
This is quite fast  about 100 mph. 