An object is dropped from rest at a height of $150\, m$ and simultaneously another object is dropped from rest at a height $100 \,m$. What is the difference in their heights after $2\,\sec $ if both the objects drop with same accelerations ? How does the difference in heights vary with time ?
Initial difference in height $=(150-100) \,m =50 \,m$
Distance travelled by first body in $2 \,s=h_{1}=0+\frac{1}{2}\, g(2)^{2}=2\, g$
Distance travelled by another body in $2 \,s=h_{2}=0+\frac{1}{2} \,g(2)^{2}=2 \,g$
After $2 \,s$, height at which the first body will be $= h _{1}^{\prime}=150-2\, g$
After $2\, s,$ height at which the second body will be $= h _{2}^{\prime}=100-2\, g$
Thus, after $2\, s$, difference in height $=150-2\, g -(100-2\, g )$
$=50 \,m =$ initial difference in height
Thus, difference in height does not vary with time.
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 ?
$(a)$ Define acceleration.
$(b)$ A stone describes a circular path with a constant speed. State the type of motion of the stone.
Write true or false for the following statements
A motion is said to be uniform, if $x \propto t^{2}$
$(a)$ 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 ?
A body is thrown vertically upward with velocity $u$, the greatest height $h$ to which it will rise is,