A motor cyclist travels a certain distance with a uniform speed of $30\, m/s$ and immediately turns back and returns to starting point with a uniform speed $20\, m/s$. Then the average speed of the motor cycle is ..........$m/s$ :-

A car travels the first half of a distance between two places at a speed of $30\, km/hr$ and the second half of the distance at $50 \,km/hr$. The average speed of the car for the whole journey is..........$km/hr$

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 $40\; min$ ?

A body has speed $V, 2V$ and $3V$ in first $1/3$ of distance $S$, seconds $1/3$ of $S$ and third $1/3$ of $S$ respectively. Its average speed will be

Position-time graph for a particle is shown in figure. Starting from $t=0$, at what time $t$ is ......... $s$, the average velocity is zero

Give difference between average speed and average velocity.