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A particle is projected at an angle of elevation \(\alpha\) and atter \(t\) second, it appears to have an angle of elevation \(\beta\) as ste from the point of projection. The initial velocity will be (1) \(\frac{g t}{2 \sin (\alpha-\beta)}\) (2) \(\frac{g t \cos \beta}{2 \sin (\alpha-\beta)}\) (3) \(\frac{\sin (\alpha-\beta)}{2 g t}\) (4) \(\frac{2 \sin (\alpha-\beta)}{g t \cos \beta}\)

Short Answer

Expert verified
The initial velocity is \( \frac{g t \cos \beta}{2 \sin (\alpha - \beta)} \), which corresponds to option (2).

Step by step solution

01

Understand the Problem Setup

A particle is projected with an initial velocity at an angle \( \alpha \) with respect to the horizontal. After \( t \) seconds, from the point of projection, the angle of elevation of the particle is \( \beta \). We need to find the initial velocity in terms of given parameters.
02

Analyze Projectile Motion

In projectile motion, the horizontal and vertical components of velocity are \( u \cos \alpha \) and \( u \sin \alpha \) respectively, where \( u \) is the initial velocity. The vertical position after \( t \) seconds is given by \( y = u \sin \alpha \cdot t - \frac{1}{2}gt^2 \).
03

Determine Projectile's Position at Time t

At time \( t \), the horizontal distance traveled is \( x = u \cos \alpha \cdot t \) and the vertical distance is \( y = u \sin \alpha \cdot t - \frac{1}{2}gt^2 \).
04

Relate Position to Angle of Elevation \( \beta \)

The angle of elevation \( \beta \) from the point of projection is given by \( \tan \beta = \frac{y}{x} = \frac{u \sin \alpha \cdot t - \frac{1}{2}gt^2}{u \cos \alpha \cdot t} \). Simplifying gives us \( \tan \beta = \frac{u \sin \alpha \cdot t - \frac{1}{2}gt^2}{u \cos \alpha \cdot t} \).
05

Express Initial Velocity \( u \)

From the relation \( \tan \beta = \frac{(u \sin \alpha) t - \frac{1}{2} g t^2}{u \cos \alpha \cdot t} \), rearranging to solve for \( u \) gives us:\( u = \frac{g t \cos \beta}{2 \sin (\alpha - \beta)} \) after using trigonometric identities to simplify the equation.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Angle of Elevation
The concept of the 'angle of elevation' is crucial in understanding projectile motion and is often used in physics problems. It refers to the angle between the horizontal line from the observer's point to the object and the line of sight to the object itself. Initially, when a particle is projected, it has an angle of elevation known as \( \alpha \). This is the angle at which the object is launched.

As the particle travels, the angle of elevation changes. After a certain time \( t \), the angle of elevation from the initial point of projection changes to \( \beta \). Calculating this requires us to consider how high and how far the object has traveled relative to its starting point.
  • The initial angle \( \alpha \) helps determine the projectile's initial path.
  • The angle \( \beta \) after \( t \) seconds gives insight into the height gained and distance covered.
  • Understanding these angles is essential for analyzing and solving physics problems involving projectile motion.
Initial Velocity
Initial velocity, noted as \( u \) in physics equations, is a critical concept in analyzing motion. It represents the speed and direction at which an object starts its motion. In the context of projectile motion, the initial velocity is divided into two components:
  • The horizontal component, \( u \cos \alpha \), which affects how far the projectile will travel horizontally.
  • The vertical component, \( u \sin \alpha \), which determines how high the projectile rises.
These components are vital in predicting the trajectory of a projectile.

In the given problem, the initial velocity affects the particle's flight path, governed by the angle of projection \( \alpha \) and the angle of elevation \( \beta \) at time \( t \). The equation for solving the initial velocity based on these parameters uses trigonometric identities to account for these angles.
Understanding how to calculate initial velocity helps in predicting the projectile's behavior in motion, making it a fundamental concept for solving physics problems related to projectiles.
Trigonometry in Physics
Trigonometry plays an integral role in physics, especially in analyzing motions like projectile motion. It allows us to break down complex motions into more manageable components based on angles and lengths. Key trigonometric functions like sine, cosine, and tangent are invaluable here.
  • The sine and cosine functions help decompose the initial velocity into vertical and horizontal components.
  • The tangent function is used to express relationships involving angles of elevation, such as \( \tan \beta = \frac{y}{x} \).
In the projectile motion problem, trigonometry is applied to simplify relations between observed angles, the velocity components, and the particle's position after time \( t \). To find the initial velocity, trigonometric identities can be employed to express the relationship between \( \alpha \) and \( \beta \), the angles of elevation.

Understanding trigonometry's application in physics helps in solving problems where angles and directional movements play a crucial role, making it easier to predict object trajectories and interactions.

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Most popular questions from this chapter

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