$(a)$ Draw velocity-time graph for the following cases
$(i)$ When the object is at rest.
$(ii)$ When the object is thrown vertically upwards.
$(b)$ A motorcyclist riding motorcycle $A$ who is travelling at $36\, km h^{-1}$ applies the brakes and stops the motorcycle in $10\, s$. Another motorcyclist of motorcycle $B$ who is travelling at $18\, km h^{-1}$ applies the brakes and stops themotorcycle in $20\, s$. Plot speed-time graph for the two motorcycles. Which of the two motorcycles travelled farther before it come to a stop ?
For motorcycle $A$,
$u=36 km h ^{-1}$
$=\frac{36 \times 5}{18}=10 ms ^{-1}$
$v=0$
$t=10 s$
For motorcycle $B,$
$u=18 km h ^{-1}$
$=\frac{18 \times 5}{18}=5 ms ^{-1}$
$v=0$
$t=20 s$
Distance travelled by $A$ before stopping
$=$ Area of triangle $OPQ$
$=\frac{1}{2} \times 10 \times 10=50 m$
Distance travelled by $B$ before stopping
$=$ Area of triangle $OMN =\frac{1}{2} \times 20 \times 5=50 m$
Hence, both motorcycles travel same distance before they come to a stop.
If the average velocity of a body is equal to mean of its initial yelocity and final velocity, then the acceleration of the body is
A driver of a train travelling at $40\, m s ^{-1}$ applies the breaks as a train enters a station. The train slows down at a rate of $2\, m s ^{-2} .$ The platform is $400\, m$ long. Will the train stop in time ?
A boy hits a football high up into the air. He runs and catches the football before it hits the ground. Which of the two, the boy or the football has had greater displacement ?
When is an object in motion considered to be a point object ?
A body moves with a velocity of $2\, m s ^{-1}$ for $5\, s$, then its velocity increases uniformly to $10\, m s ^{-1}$ in next $5\, s.$ Thereafter, its velocity begins to decrease at a uniform rate until it comes to rest after $5\, s$.
$(i)$ Plot a velocity-time graph for the motion of the body.
$(ii)$ From the graph, find the total distance covered by the body after $2\, s$ and $12\, s$.