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The trajectory of a projectile near the surface of the earth is given as y = 2x - 9x². If it were launched at an angle θ₀ with speed v₀ then (g = 10 m s⁻²)

Asked in JEE Main 12th April 1st Shift 2019 · Equation of the trajectory

• (1) θ₀ = cos⁻¹(1/(√5)) and v₀ = 5/3 m s⁻¹
• (2) θ₀ = sin⁻¹(1/(√5)) and v₀ = 5/3 m s⁻¹
• (3) θ₀ = cos⁻¹(2/(√5)) and v₀ = 3/5 m s⁻¹
• (4) θ₀ = sin⁻¹(2/(√5)) and v₀ = 3/5 m s⁻¹

Step-by-step solution

Why the other options are wrong

• (2) Swaps sine and cosine: tan θ₀ = 2 gives sin θ₀ = 2/√5, cos θ₀ = 1/√5.
• (3) Wrong angle and inverted speed.
• (4) Right angle written as a sine, but the speed is inverted.

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