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Apply the modelling of projectile motion to quantitatively derive the relationships
Diagram of projectile motion :
In the diagram :
- Hl : launch height
- Vi : initial velocity
- Vf : final velocity
- θ: launch angle
- H: maximum height
- The distance AB is the ‘horizontal range of the projectile’ .
- The time taken for projectile to travel along the trajectory from O to B is ‘time of flight’
Throughout the motion the vertical movement is affected by gravitational acceleration g = 9.8ms-2
To analyse the quantitative relationships between the variables :
- The vertical and horizontal component of the initial velocity depends on the launch angle
- Horizontal component : Vix = Vi × cos θ
- Vertical component : Viy = Vi × sin θ
- Relationship between max height, launch height, initial velocity and launch angle
- max height is when vertical component of velocity is zero
- Vy2 = Vy2 – 2g(H-Hl) where is Vy vertical velocity and H is height
- So when Vy=0, then
- substituting Viy = Vi × sin θ, max height can be given by
- Relationship between time of flight . initial velocity, angle of launch and launch height
- time of flight is the time taken for the vertical component of the projectile to reach max height and reach the bottom.
- using equation :
- where
- relation
- so time :
- Horizontal range of projectile
- Since the horizontal component of projectile does not experience any acceleration , the horizontal velocity remains constant .
- So horizontal range is simply Horizontal component of speed X time of flight
- Final velocity can be calculated by
- Energy consideration (Conservation of mechanical energy)
Extract from Physics Stage 6 Syllabus © 2017 NSW Education Standards Authority (NESA)