The displacement of a particle at time 't' is $s=t^{3}-4 t^{2}-5 t$, then the velocity of the particle at…

The displacement of a particle at time 't' is $s=t^{3}-4 t^{2}-5 t$, then the velocity of the particle at $t=2 \mathrm{sec}$. is
  1. $\left(\frac{1}{9}\right)$ units $/ \mathrm{sec}.$
  2. $-9$ units $/ \mathrm{sec}$
  3. 9 units $/ \mathrm{sec}$.
  4. $\left(\frac{-1}{9}\right)$ units $/$ sec.

Solution

Given $s=t^{3}-4 t^{2}-5 t$ $\therefore \frac{d s}{d t}=3 t^{2}-8 t-5$ At $t=2, \quad v=\frac{d s}{d t}=3(4)-8(2)-5=12-16-5=-9$

Asked in: MHT CET 2020 (12 Oct Shift 2)

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