MDCAT Physics · Physics · Force and motion. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
A projectile is a body that moves freely under gravity after it has been thrown. The idea to hold is that its horizontal and vertical motions are independent.
Horizontally no force acts (air resistance is ignored), so the horizontal velocity v cos θ never changes. Vertically the body has a constant acceleration g downwards, so the vertical velocity starts at v sin θ, falls to zero at the top and then grows downwards. Together these give a curved path called a parabola.
On level ground the range is greatest for a launch angle of 45°. Two angles that add up to 90°, such as 30° and 60°, give the same range but different heights and times of flight.
Students say the velocity is zero at the highest point. Only the vertical part is zero; the projectile still moves horizontally at v cos θ.
Answer: Time of flight 2.0 s, maximum height 5.0 m, range about 35 m.
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