Let x = x ( t ) and y = y ( t ) be solutions of the differential equations dx dt + ax = 0 and dy dt + by = 0…

Let x=x(t) and y=y(t) be solutions of the differential equations dxdt+ax=0 and dydt+by=0 respectively, a,bR. Given that x(0)=2 ; y(0)=1 and 3 y(1)=2 x(1), the value of t, for which x(t)=y(t), is :
  1. log232
  2. log43
  3. log34
  4. log432

Solution

Given: dxdt+ax=0

dxx=-adt

Integrating both sides,

dxx=-adt

log|x|=-at+c

At t=0,x=2

log2=0+c

logx=-at+log2

logx-log2=-at

logx2=-at

x2=e-at

x=2e-at   ...(i)

It is also given that, dydt+by=0

dyy=-bdt

log|y|=-bt+λ

At, t=0,y=1

0=0+λ

y=e-bt   ...(ii)

According to question,

3 y(1)=2 x(1)

3e-b=22e-a

ea-b=43

For xt=yt

2e-at=e-bt

2=e(a-b)t

2=43t

log2=t×log43

log432=t

Asked in: JEE Main 2024 (27 Jan Shift 1)

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