Kinematics: given 2 position vectors, time, and V of earlier

[Dillon Keeler]

If you know the position vectors of a particle at two points along its path, change in time between the two positions, and the particle's velocity at the earlier point, what quantities can you calculate?

a)average acceleration
b)final velocity
c)average velocity
d)displacement

My answer was all of the above because one can find
d) by just the two position vectors
c) by ( displacement / change in time )
b) by Vaverage= (1/2)(Vinitail+Vfinal)
a) by average acceleration = ( change in velocity / change in time)

however the answer is just c) and d). Am I forgetting to take something in consideration?

 

[nasu]

Your "b" is true only for a special case. It is not a generally valid relationship.
Do you know what is this special case? What is the condition to have this relationship?

 

[Dillon Keeler]

Your "b" is true only for a special case. It is not a generally valid relationship.
Do you know what is this special case? What is the condition to have this relationship?

Constant Acceleration?