$A$ car moves for half of its time at $80 \, km/h$ and for the rest half of the time at $40 \, km/h$. The total distance covered is $60 \, km$. What is the average speed of the car in $km/h$?

$A$ particle moves in the east direction with $15 \, m/s$ for $2 \, s$,then moves northward with $5 \, m/s$ for $8 \, s$. The average velocity of the particle is:

$A$ particle moves along a semicircle of radius $10\,m$ in $5$ seconds. The average velocity of the particle is...........$m/s$.

$A$ train travels from city-$A$ to city-$B$ with a constant speed of $18 \,ms^{-1}$ and returns back to city-$A$ with a constant speed of $36 \,ms^{-1}$. Find its average speed during the journey. (in $\,ms^{-1}$)

$A$ man walks on a straight road from his home to a market $2.5 \; km$ away with a speed of $5 \; km \; h^{-1}$. Finding the market closed,he instantly turns and walks back home with a speed of $7.5 \; km \; h^{-1}$. What is the average speed of the man over the interval of time $0$ to $30 \; min$?

Define velocity. Define average velocity.