The displacement x of a particle varies wi

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The displacement $x$ of a particle varies with time $t,x = a{e^{ - \alpha t}} + b{e^{\beta t}}$, where $a,\,b,\,\alpha \,{\rm{and }}\beta $ are positive constants. The velocity of the particle will

A

Go on decreasing with time

B

Be independent of $\alpha $ and $\beta $

C

Drop to zero when $\alpha = \beta $

D

Go on increasing with time

The displacement $x$ of a particle varies with time $t,x = a{e^{ - \alpha t}} + b{e^{\beta t}}$, where $a,\,b,\,\alpha \,{\rm{and }}\beta $ are positive constants. The velocity of the particle will

$x = a{e^{ - \alpha t}} + b{e^{\beta t}}$

Velocity $v = \frac{{dx}}{{dt}} = \frac{d}{{dt}}(a{e^{ - \alpha t}} + b{e^{\beta t}})$

$ = a.{e^{ - \alpha t}}( - \alpha ) + b{e^{\beta t}}.\beta )$ $ = - a\alpha {e^{ - \alpha t}} + b\beta {e^{\beta t}}$

Acceleration $ = - a\alpha {e^{ - \alpha t}}( - \alpha ) + b\beta {e^{bt}}.\beta $

$ = a{\alpha ^2}\,{e^{ - \alpha t}} + b{\beta ^2}{e^{\beta \,t}}$

Acceleration is positive so velocity goes on increasing with time.