Question:

An aircraft is flying at a height of $3400\, m$ above the ground. If the angle subtended at a ground observation point by the aircraft positions $10\,s$ apart is $30^\circ$ then the speed of the aircraft is

Updated On: Mar 4, 2024
  • $ 19.63\,m{{s}^{-1}} $
  • $ 196.3\,m{{s}^{-1}} $
  • $ 108\,m{{s}^{-1}} $
  • $ 1963\,m{{s}^{-1}} $
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The Correct Option is B

Solution and Explanation

$O$ is the observation point at the ground. $A$ and $B$ are the positions of aircraft for which $? AOB=30^?$.
Time taken by aircraft from $A$ to $B$ is $10\,s$.
In $\Delta AOB,$
$tan\,30^{?}$
$=\frac{AB}{3400}$
$AB=3400\,tan\,30^{?}$
$=\frac{3400}{\sqrt{3}}m$
$\therefore$ Speed of aircraft, $v=\frac{AB}{10}$
$=\frac{3400}{10\sqrt{3}}$
$=196.3\,ms^{-1}$
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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