Question:

From a tower of height $H$, a particle is thrown vertically upwards with a speed $u$. The time taken by the particle to hit the ground, is $n$ times that taken by it to reach the highest point of its path. The relation between $H, u$ and $n$ is

Updated On: Sep 27, 2024
  • $2gH = n^2u^2$
  • $ gH = (n-2)^2 u^2$
  • $2gH = nu^2 (n-2)$
  • $ gH = (n-2)u^{2}$
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The Correct Option is C

Solution and Explanation

Time taken to reach highest point is $t_{1}=\frac{u}{g}$
Speed on reaching ground $=\sqrt{u^{2}+2gh}$
Now, $v=u+at$
$\Rightarrow \sqrt{u^{2}+2 g h}=-u+gt$
$\Rightarrow t=\frac{u+\sqrt{u^{2}+2 g H}}{g}=\frac{nu}{g}$
$\Rightarrow 2gH=n(n-2) u^{2}$

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Concepts Used:

Motion in a straight line

The motion in a straight line is an object changes its position with respect to its surroundings with time, then it is called in motion. It is a change in the position of an object over time. It is nothing but linear motion. 

Types of Linear Motion:

Linear motion is also known as the Rectilinear Motion which are of two types:

  1. Uniform linear motion with constant velocity or zero acceleration: If a body travels in a straight line by covering an equal amount of distance in an equal interval of time then it is said to have uniform motion.
  2. Non-Uniform linear motion with variable velocity or non-zero acceleration: Not like the uniform acceleration, the body is said to have a non-uniform motion when the velocity of a body changes by unequal amounts in equal intervals of time. The rate of change of its velocity changes at different points of time during its movement.