A lacrosse ball that is thrown straight upwards reaches a maximum height of 4.5 m. At what initial velocity was it thrown? (note: final velocity, v = 0, at the top).

The initial velocity was 9.39 m/s

Explanation:

Lets explain how to solve the problem

The ball is thrown straight upward with initial velocity u

The ball reaches a maximum height of 4.5 m

At the maximum height velocity v = 0

The acceleration of gravity is - 9.8 m/s²

We need to find the initial velocity

The best rule to find the initial velocity is v² = u² + 2ah, where v is

the final velocity, u is the initial velocity, a is the acceleration of

gravity and h is the height

⇒ v = 0, h = 4.5 m, a = - 9.8 m/s²

⇒ 0 = u² + 2 (-9.8) (4.5)

⇒ 0 = u² - 88.2

Add 88.2 to both sides

⇒ 88.2 = u²

Take square root for both sides

⇒ u = 9.39 m/s

The initial velocity was 9.39 m/s