Lesson · P.1.3

Projectile motion

How the time a horizontally launched object spends in the air depends only on how far it falls, h = 1/2 × g × t², and how that time then unlocks the horizontal distance it travels, x = v × t, the two-step calculation the HESI A2 physics subtest builds every projectile question around.

ObjectiveP.1.3Read4 minExam weightMotion ≈ 24% of Physics

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What you will be able to do

You can explain why an object's horizontal velocity stays constant in flight while its vertical velocity keeps accelerating under gravity.
You can find how long a horizontally launched object stays in the air from its drop height alone, using h = 1/2 × g × t².
You can chain that time into the horizontal distance travelled, using x = v × t, to solve a full projectile problem in two steps.

What the lesson concludes

Horizontal velocity and vertical velocity are independent. Only gravity acts on the vertical part of the motion.
Time of flight comes from the height alone, using h = 1/2 × g × t², and has nothing to do with how fast the object is moving forward.
Once you have the time, horizontal distance is one multiplication: x = v × t.
A horizontal launch starts with zero vertical velocity, so it falls exactly like a dropped object while still carrying forward at a constant speed.
Use g = 9.8 m/s² unless a question gives you a different value for gravity.