Answer the following questions related to linear momentum.
a. (a) Define linear momentum and state its SI unit.
b. (b) Explain why linear momentum is treated as a vector quantity and how its direction is decided for a moving body.
c. (c) A loaded truck and a small car are found to possess equal magnitudes of linear momentum while moving on a straight road. Which vehicle is moving with the higher speed? Give a reason for your answer without using numerical calculations.
d. (d) If the velocity of a body is reversed while its speed remains unchanged, describe qualitatively how its momentum is affected.