In projectile motion, why we take y-component for 'TF'?

[Indranil]

In projectile motion, we have two components one is x and another is y. x = u cosθ and y = u sinθ
But why do I take the' y' component for calculating the 'time of flight' not the 'x' component?
y = ut sinθ - 1/2 gt^2, t = 2u sinθ / g

 

[Doc Al]

What determines the "time of flight" is when it hits the ground. And that involves the vertical motion. (If it only moved horizontally, then it would never hit the ground.)

 

[Chandra Prayaga]

What is meant by "time of flight?"

 

[jbriggs444]

What is meant by "time of flight?"

The elapsed time between launch and impact. Start a stopwatch when the projectile is launched. Stop it when it lands. The reading on the stopwatch is the "time of flight".

 

[Indranil]

What is meant by "time of flight?"

When a particle projected from any point [consider O] and reaches the same horizontal plane at any point [consoder B]. The total time taken to reach B is the time of flight.