A river flows due east at 1.50 m/s. A boat crosses the river from the south shore to the north shore by maintaining a constant velocity of 10 m/s due north relative to the water.(a) What is the velocity of the boat relative to the shore?(b) If the river is 300 m wide, how far downstream has the boat moved by the time it reaches the north shore?

Respuesta :

Answer:

a

   [tex]u = 10.11 \ m/s[/tex]

b

   [tex]x = 44.996 \ m[/tex]    

Explanation:

From the question we are told that    

        The velocity of the river due east is  [tex]v = 1.150i \ m /s[/tex]

        The velocity of the boat due north is  [tex]v_1 = 10j \ m/ s[/tex]

         The width of the river is  [tex]d = 300 \ m[/tex]

Generally the velocity of the boat relative to the shore

           [tex]u = \sqrt{v^2 + v_1^2}[/tex]

=>        [tex]u = \sqrt{1.50 ^2 + 10^2}[/tex]

=>        [tex]u = 10.11 \ m/s[/tex]

Generally direction of the boat relative to the shore is mathematically represented as

           [tex]tan \theta = \frac{v}{v_1}[/tex]

=>        [tex]\theta = tan^{-1}[ \frac{v}{v_1}][/tex]

=>        [tex]\theta = tan^{-1}[ \frac{1.5}{10}][/tex]

=>        [tex]\theta = 8.53^o[/tex]

Generally the distance covered by the boat in the direction of flow of the river before reaching the north shore is mathematically represented as

             [tex]x = d* tan(\theta )[/tex]

=>          [tex]x = 300 * tan(8.53)[/tex]

=>         [tex]x = 44.996 \ m[/tex]          

         

(a) The velocity of the boat relative to the shore is 10.11 m/s.

(b) The distance traveled by the boat when it reaches the north shore is 303.3 m.

The given parameters;

  • initial velocity of the river, = 1.5 m/s due east
  • velocity of the boat, = 10 m/s due north

(a) The velocity of the boat relative to the shore is calculated by applying Pythagoras theorem as shown below;

[tex]v = \sqrt{1.5^2 + 10^2} \\\\v = 10 .11 \ m/s[/tex]

(b) Let the time taken for the boat to reach the north shore = t

[tex]distance = speed \times time \\\\c^2 = a^2 + b^2\\\\[/tex]

  • the width of the river is the height of the right-triangle
  • the displacement of the river after time "t" is the base of the right-triangle
  • the displacement of the boat after time "t" is the hypotenuse side

[tex](10.11t)^2 = (300)^2 + (1.5t)^2\\\\102.21t^2 = 90,000 + 2.25t^2\\\\99.96t^2 = 90,000\\\\t^2 = \frac{90,000}{99.96} \\\\t^2 = 900\\\\t = \sqrt{900} \\\\t = 30 \ s[/tex]

The distance traveled by the boat when it reaches the north shore;

[tex]d = 10.11t\\\\d = 10.11 \times 30\\\\d = 303.3 \ m[/tex]

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