Answer
(a) $300m$
(b) $30s$
Work Step by Step
(a) We know that the longest possible wavelength gives the constructive radio wave and it is equal to the path difference of the two sources and the observed point. Thus,
$\lambda=450m-150m=300m$
(b) We know that
$l_1=\sqrt{(150m)^2+(vt)^2}$....eq(1)
and $l_2=\sqrt{(150m)^2+(vt)^2}$...eq(2)
adding eq(1) and eq(2), we obtain:
$\sqrt{(150m)^2+(vt)^2}+\sqrt{(150m)^2+(vt)^2}=150m$
This simplifies to:
$t=29.59s$
$\implies t=30s$
