When is an object said to be in motion?

Your friend driving his car overtakes your car on the highway. Which of the following statements must be true at the instant he is passing you? Assume the cars as point particles.

The magnitude of the displacement is equal to the distance covered in a given interval of time if the particle

When is an object said to be a particle?

Under what condition is the magnitude of distance covered by an object equal to its displacement?

The position vector of a moving particle at time $t$ is $r = 3 \hat{i} + 4t \hat{j} - t \hat{k}$. Its displacement during the time interval $t = 1 \ s$ to $t = 3 \ s$ is