Question:

A hiker stands on the edge of a cliff $490\,m$ above the ground and throws a stone horizontally with a speed of $15\,ms^{-1}$. The time taken by the stone to reach the ground is

Updated On: Jul 5, 2022
  • $5\,s$
  • $10\,s$
  • $12\,s$
  • $15\,s$
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The Correct Option is B

Solution and Explanation

Here, $u = 15\,m \,s^{-1}$, $h = 490\,m$ Time taken by the stone to reach the ground is $t=\sqrt{\frac{2h}{g}}$ $=\sqrt{\frac{2\times490\,m}{9.8\,ms^{-2}}}$ $=10\,s$
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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