# The motion of a particle along a straight line is described by equation x = 8 + 12t – t^3 where, x is in metre and t in sec . The retardation of the particle when its velocity becomes zero  is

Q:The motion of a particle along a straight line is described by equation
x = 8 + 12t – t3 . where, x is in metre and t in sec. The retardation of the particle when its velocity becomes zero  is
(a) 24 ms–2

(b) zero

(c) 6 ms–2

(d) 12 ms–2

Ans: (d)

Sol: x = 8 + 12t – t3

Differentiating w.r.t. time

$\displaystyle \frac{dx}{dt} = 0 + 12-3t^2$

$\displaystyle v = 12-3t^2$

When v = 0 ; t = 2 sec

Again differentiating with time

$\displaystyle \frac{dv}{dt} = 0-6t$

$\displaystyle a = -6t$

a = -12 m/s2