A train starting from rest travels the first part of its journey with constant acceleration $a$ , second part with constant velocity $v$ and third part with constant retardation $a$ , being brought to rest. The average speed for the whole journey is $\frac{{7v}}{8}$. The train travels with constant velocity for $...$ of the total time

Two points move in the same straight line starting at the same moment from the same point in it. The first moves with constant velocity $u$ and the second with constant acceleration $f$. During the time elapses before the second catches, the first greatest distance between the particle is $........$

The acceleration of a particle is increasing linearly with time $t$ as $bt$. The particle starts from the origin with an initial velocity ${v_0}$. The distance travelled by the particle in time $t$ will be

A body $A$ starts from rest with an acceleration ${a_1}$. After $2$ seconds, another body $B$ starts from rest with an acceleration ${a_2}$. If they travel equal distances in the $5$th second, after the start of $A$, then the ratio ${a_1}:{a_2}$ is equal to

Explain the acceleration.

Displacement $(x)$ of a particle is related to time $(t)$ as:

$x = at + bt^2 -ct^3$

where $a, b$ and $c$ are constants of the motion. The velocity of the particle when its acceleration is zero is given by