I know that there's 5 key equations for motion which is: d = (vf+vi/2)t vf = vi + at d = vit + 1/2at^2 vf^2 = vi^2 + 2ad d = vft - 1/2at^2 Correct? But my teacher was confusing me today and he taught us these two other equations: d = 1/2(vi+vf)t d = 1/2at^2 What are these? Are they just other "rules of motion" like everything else?
The second equation 'D=1/2at^2' is one of the kinematic equations 'D=Vi+1/2at^2' where the initial velocity 'Vi' is considered to be zero.
This one is incorrect. Either your teacher or you copied it wrong. This is the correct version, assuming you meant (1/2)(v_{i}+v_{f})t. Actually, only two equations are essential: v_{f} = v_{i} + at d = v_{i}t + (1/2)at^{2} The others can be derived from these two.
5 eq v final velocity u initial vel. t time s displacement a constant acc^{n} v= u +at s= ut + .5at^{2} v^{2}= u^{2} +2as s= vt - .5at^{2} s= .5(v+u)t
but while doing numerical it is irritating to first get acceleration, so actually 5 eq^{n} are good adding to it this gives feel to a child what he's doing also kinematics it a beginning so one can learn these quickly as afterward formula formula formula!!!
True, but I like those two because if you know calculus you can get them by integrating d^{2}x/dt^{2} = a twice. Of course, that means you really need to remember only one equation which basically just says "acceleration is constant."