Question:

A projectile is given an initial velocity of $(\hat{i} + 2\hat{j}) m/s$, where $\hat{i}$ is along the ground and $\hat{j}$ is along the vertical. If $g = 10 m/s^2$, then the equation of its trajectory is

Updated On: Oct 1, 2024
  • $y=x-5x^2$
  • $y=2x-5x^2$
  • $4y=2x-5x^2$
  • $4y=2x-25x^2$
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The Correct Option is B

Solution and Explanation

Initial velocity = (i + 2j)m/s
Magnitude of initial velocity u =$\sqrt{(1)^2+(2)^2}=\sqrt 5 m/s$
Equation of trajectory of projectile is
$ \, \, \, \, y=x tan \theta -\frac{gx^2}{2u^2}(1+tan^2\theta)\bigg[tan \theta=\frac{y}{x}=\frac{2}{1}=2\bigg]$
$\therefore \, \, \, y=x \times 2-\frac{10(x)^2}{2(\sqrt 5)^2}[1+(2)^2]$
$ \, \, \, \, \, \, \, \, \, \, \, \, =2x-\frac{10(x^2)}{2 \times 5}(1+4)$
$ \, \, \, \, \, \, \, \, \, \, \, \, 2x-5x^2$
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Questions Asked in JEE Main exam

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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