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

The position of an object moving along the $x$-axis is given by $x = a + b t^2$,where $a = 8.5 \; m$,$b = 2.5 \; m s^{-2}$,and $t$ is measured in seconds. What is the average velocity between $t = 2.0 \; s$ and $t = 4.0 \; s$ (in $; m s^{-1}$)?

$A$ person walks along a straight road from his house to a market $2.5 \,km$ away with a speed of $5 \,km/h$ and instantly turns back and reaches his house with a speed of $7.5 \,km/h$. The average speed of the person during the time interval $0$ to $50 \,min$ is (in $m/s$)

The position of an object moving along the $X$-axis is given by $x = \alpha + \beta t^2$, where $\alpha$ and $\beta$ are constants with appropriate dimensions and $t$ is time in seconds. The average velocity between $t = 2 \ s$ and $t = 4 \ s$ is $12 \ m/s$. If $\alpha = 8 \ m$, then the value of $\beta$ is: (in $m/s^2$)

If the average velocity of a particle moving on a straight line is zero in a time interval,then:

Give the difference between average speed and average velocity.