Projectile on a downward inclined plane — time of flight dependence The time of flight of a projectile launched on a downward inclined plane depends on which parameters?

Introduction / Context:
Projectile motion on an inclined plane is a classic kinematics problem. Unlike level-ground trajectories, the landing condition depends on the plane’s slope as well as the projectile’s launch parameters.

Given Data / Assumptions:

• Initial speed u, launch angle α measured from the horizontal.
• Plane inclined downward at angle β from the horizontal (β > 0).
• Uniform gravity g; no air resistance; point-mass projectile.

Concept / Approach:
Resolve motion into horizontal and vertical components, then impose the landing condition that the projectile meets the inclined plane. The intersection occurs when the projectile’s parametric equation satisfies y = x * tan(−β), which links both α and β in the time-of-flight expression.

Step-by-Step Solution:

Verification / Alternative check:
When β = 0 (level ground), the expression reduces to t = 2u sin α / g, the standard formula, confirming consistency. Increasing downward slope (β larger) generally increases the time of flight for fixed α and u until geometric limits apply.

Why Other Options Are Wrong:

• Angle of projection only / plane angle only: Each alone is insufficient; the intersection condition couples both angles.
• None of these / initial speed only: Incorrect; both geometric angles matter besides u and g.

Common Pitfalls:
Forgetting to change the landing condition to match the inclined plane; mixing angle definitions (from horizontal vs. from plane).

Final Answer:
Both (angle of projection) and (angle of inclination of the plane)