The average time taken by a normal person to react to an emergency is one$-$fifteenth of a second and is called the 'reaction time'. If a bus is moving with a velocity of $60\, km h^{-1}$ and its driver sees a child running across the road, how much distance would. the bus had moved before he could press the brakes ? The reaction time of the people increases when they are intoxicated. How much distance had the bus moved if the reaction time of the driver were $\frac{1}{2}\, s$ under the influence of alcohol ?

Out of the three speed$-$time graphs shown below

Identify the graph for the following cases.

$(i)$ A ball thrown vertically upwards and returning to the hand of the thrower ?

$(ii)$ A body decelerating to a constant speed and accelerating.

$(a)$ Write differences between speed and velocity.

$(b)$ The speed of a moving object is $x m s ^{-1}$. Its velocity is $y m s ^{-1}$. What is the similarity observed ?

The distance$-$time graph of a body is a straight line inclined to time axis. The body is in

Account for the following

$(a)$ Name the quantity which is measured by the area occupied below the velocity$-$time graph.

$(b)$ An object is moving in a certain direction with acceleration in the perpendicular directions.

$(c)$ Under what condition is the magnitude of average velocity of an object equal to its average speed ?

$(d)$ An example of uniformly accelerated motion.

$(e)$ A body is moving along a circular path of radius

$(r)$. What will be the distance and displacement of the body when it completes half revolution ?