Answer:137.48 s
Explanation:
Given
Width of river=1.5 km
velocity of river=5 km/h
velocity of boat w.r.t river =12 km/h
To cross the river in minimum time hunter needs to cross the river perpendicular to the flow
i.e. velocity of boat w.r.t water must be perpendicular
i.e. x component of boat must be equal to river flow
[tex]12cos\theta =5[/tex]
where [tex]\theta [/tex] is angle made by boat w.r.t bank
[tex]cos\theta =\frac{5}{12}[/tex]
[tex]cos\theta =0.416[/tex]
[tex]\theta =65.417^{\circ}[/tex]
its vertical component is [tex]12sin(65.417)=10.91 m/s[/tex]
Time taken[tex]=\frac{1.5\times 1000}{10.91}=137.48 s[/tex]
