Two projectiles are launched with the same initial speed from the same location, one at a 30° angle and the other at a 60° angle with the horizontal. They land at the same height at which they were launched. If air resistance is negligible, how do the projectiles’ respective maximum heights, H30 and H60 , and times in the air, T30 and T60 , compare with each other?

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Answer:

Explanation:

Given

launch angle [tex]\theta _1=30^{\circ}[/tex]

[tex]\theta _2=60^{\circ}[/tex]

[tex]\theta _1[/tex] and [tex]\theta _2[/tex] are complimentary angles so range for both of them is same

[tex]H_{max}=\frac{u^2(\sin \theta )^2}{2g}[/tex]

[tex]H_{30}=\frac{u^2(\sin 30)^2}{2g}[/tex]

[tex]H_{30}=\frac{u^2}{8g}[/tex]

time of flight [tex]=\frac{2u\sin \theta }{g}[/tex]

[tex]t_{30}=\frac{u}{g}[/tex]

For [tex]\theta =60^{\circ}[/tex]

[tex]H_{60}=\frac{u^2(\sin 60)^2}{2g}[/tex]

[tex]H_{60}=\frac{3u^2}{8g}[/tex]

[tex]t_{60}=\frac{2u\sin 60}{g}=\frac{\sqrt{3}u}{g}[/tex]

[tex]H_{60}=3\times H_{30}[/tex]

[tex]t_{60}=\sqrt{3}\times t_{30}[/tex]

The projectile launched at 60° attained more height and also spent more time in air when compared to the projectile launched at 30° to the horizontal.

The given parameters;

  • angle of projection of the first projectile, θ₁ = 30⁰
  • angle of projection of the second projectile, θ₂ = 60⁰

The maximum height reached by each projectile is calculated as follows;

[tex]H= \frac{u^2 (sin\ \theta)^2}{2g} \\\\H_{30} = \frac{u^2 (sin \ 30)^2}{2\times 9.8}\\\\H_{30} = 0.0128 \ u^2[/tex]

[tex]H= \frac{u^2 (sin\ \theta)^2}{2g} \\\\H_{60} = \frac{u^2 (sin \ 60)^2}{2\times 9.8}\\\\H_{60} = 0.0383 \ u^2[/tex]

The time of flight of the two projectiles is calculated as follows;

[tex]T = \frac{2u\times sin(\theta)}{g} \\\\T_{30} = \frac{2u \times sin( 30)}{9.8} \\\\T_{30} = 0.102 \ u[/tex]

[tex]T_{60} = \frac{2u \times sin( 60)}{9.8} \\\\T_{60} = 0.177 \ u[/tex]

Thus, the projectile launched at 60° attained more height and also spent more time in air when compared to the projectile launched at 30° to the horizontal.

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