1- Speed is the modulus or magnitude (scalar) of the velocity (vector)
2- Motion is the length of the trajectory followed while displacement is the final position - the initial position, xf-x0.
3- Here it's referring to the linear momentum. An object moving in a straight line has a momentum p=m*v. Where m is the mass of the object and v is the velocity.
4- Acceleration is the rate of change of velocity with respect to time. a=dv/dt.
