Chapter 3.1, Problem 3.1TYU

In which of these situations would the average velocity vector ${\stackrel{\to }{v}}_{\text{av}}$ over an interval be equal to the instantaneous velocity $\stackrel{\to }{v}$ at the end of the interval? (i) A body moving along a curved path at constant speed; (ii) a body moving along a curved path and speeding up; (iii) a body moving along a straight line at constant speed; (iv) a body moving along a straight line and speeding up.