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 (in $km/h$) of the man over the interval of time $0$ to $50\; min$ ?

A particle moving in a straight line covers half the distance with speed of $3 \,m/s$. The other half of the distance is covered in two equal time intervals with speed of $4.5 \,m/s$ and $7.5 \,m/s$ respectively. The average speed of the particle during this motion is…… $\,m/s$

Velocity of an object in rectilinear motion is given as function of time by $v = t -t^3$, where $v$ is in $m/s$ and $t$ is in seconds. Its average velocity over the time interval from $t = 0\ s$ to $t = 2\ s$ is……..$m/s$

A particle moves for $20 \,seconds$ with velocity $3 \,m/s$ and then velocity $4\, m/s$ for another $20 \,seconds$ and finally moves with velocity $5 \,m/s$ for next $20\, seconds$. What is the average velocity of the particle……….$m/s$

One car moving on a straight road covers one third of the distance with $20 \,km/hr $ and the rest with $60\, km/hr$. The average speed is……….$km/hr$