velocity Is the time rate of change of ___.

Acceleration is the time rate of change of _____.

What is the expression for rate of change of momentum?

Why is not the direction of rate of change of momentum always in the direction of momentum?

A particle travelling along a straight line traversed one third of the total distance with velocity 4m//s . The remaining part of the distance was covered with a velocity 2m//s for half of the time and with velocity 6m//s for the other half of the time. What is the average velocity for the whole motion.