A bus decreases its speed from $80\, km\, h^{-1}$ to $50 \,km h ^{-1}$ in $4\, s$. Find the acceleration of the bus.

$(a)$ 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 ?

A girl walks along a straight path to drop a letter in the letterbox and comes back to her initial position. Her displacement-time graph is shown in Fig. Plot a velocity – time graph for the same.

$(a)$ Define uniform circular motion.

$(b)$ Ram goes for a morning walk in a circular park daily. He completes one revolution of the park in $4$ minutes. Find his speed if the diameter of the park is $420\, m$.

$(c)$ Draw velocity$-$time graph for uniform motion along a straight line. How can you find distance covered by a body from this graph ?

An electron moving with a velocity of $5 \times 10^{4}\, ms ^{-1}$ enters into a uniform electric field and acquires a uniform acceleration of $10^{4}\, ms ^{-2}$ in the direction of its initial motion.

$(i)$ Calculate the time in which the electron would acquire a velocity double of its initial velocity.

$(ii)$ How much distance the electron would cover in this time ?