Kinetic energy or momentum?
I don't know why I noticed this a few days ago (tomorrow is my exam), I've been using kinetic energy and momentum for 3 courses now >.>
Someone please help explain when I should use momentum vs kinetic energy..
a car of mass m collides with a stationary truck of mass M
the car's initial velocity is Vi. The car's final velocity is 0
find the truck's final velocity
so if I do momentum
p1i + p2i = p1f + p2f
p1i + 0 = 0 + p2f
mVi = MVf
(m/M)*Vi = Vf
But if I use kinetic energy
K1i + K2i = K1f + K2f
K1i + 0 = 0 + K2f
0.5*m*Vi^2 = 0.5*M*Vf^2
[(m/M)*Vi^2]^0.5 = Vf or Vf = Vi*((m/M)^0.5)
^0.5 is square root
Clearly, I got a different answer....