Question:

The width of river is 1 km. The velocity of boat is 5 km/hr. The boat covered the width of river with shortest will possible path in 15 min. Then the velocity of river stream is:

Updated On: Oct 5, 2023
  • \(3 \ km/hr\)

  • \(4 \ km/hr\)

  • \(\sqrt {29} \ km/hr\)

  • \(\sqrt {41} \ km/hr\)

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The Correct Option is A

Solution and Explanation

\(t=\frac {d}{\sqrt {υ^2-v^2}}\)

\(\frac 14= \frac {1}{\sqrt {(5)^2-v^2}}\)

\(\frac {1}{16} = \frac {1}{25-v^2}\)

\(25-v^2 = 16\)

\(v^2 = 9\)

\(v =\sqrt  {9}\)

\(v=3\ km/hr\)

So, the correct option is (A): \(3\ km/hr\)

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Concepts Used:

Motion in a Plane

It is a vector quantity. A vector quantity is a quantity having both magnitude and direction. Speed is a scalar quantity and it is a quantity having a magnitude only. Motion in a plane is also known as motion in two dimensions. 

Equations of Plane Motion

The equations of motion in a straight line are:

v=u+at

s=ut+½ at2

v2-u2=2as

Where,

  • v = final velocity of the particle
  • u = initial velocity of the particle
  • s = displacement of the particle
  • a = acceleration of the particle
  • t = the time interval in which the particle is in consideration