A body starts with an initial velocity of $10 \mathrm{m} {\mathrm{s}}^{-1}$ and moves along a straight line with a constant acceleration. When the velocity of the particle becomes $50 \mathrm{m} {\mathrm{s}}^{-1}$ the acceleration is reversed in direction without changing magnitude. Find the speed of the particle in $\mathrm{m} {\mathrm{s}}^{-1}$ when it reaches the starting point.

The acceleration time plot for a particle (starting from rest) moving on a straight line is shown in the figure. For given time interval,

A particle moves along the $Y$ -axis and its $y$ -coordinate $\left(y\right)$changes with time $\left(t\right)$ as $y=u(t-2)+a(t-2{)}^2$.

The graph below gives the coordinator of a particle travelling along the $X-$axis as a function of $\tan \theta$. $AM$ is the tangent to the curve at the starting moment and $BN$ is tangent at the end moment $\left({\theta }_1={\theta }_2=120°\right)$

The direction $(i$ or $-i)$ of acceleration during the first $10$ seconds is