Question

A ball is thrown vertically upwards reaches a height of 80m
calculate the time to reach highest point and
the speed of the ball upon arrival on the ground.

Answer 1

Initial speed of ball is 40 m/s and time to reach highest point is 4 seconds.

Solution

Here height (h) = 80 m

Final speed of ball = 0 m/s

Gravitational acceleration (g) = -10 m/s²

We will use 3rd equation of motion to find initial speed of ball :

* 3rd equation → v² - u² = 2gh

⇒ 0² - u² = 2 × 80 × (-10)

⇒ 0 - u² = -1600

⇒ u² = 1600

⇒ u = √1600

⇒ u = 40 m/s

∴ Initial speed of ball = 40 m/s.

Now we will use 1st equation of motion to find time taken to reach highest position.

* 1st equation → v = u + gt

⇒ 0 = 40 + (-10)t

⇒ 0 = 40 - 10t

⇒ 10t = 40

⇒ t = 40/10

⇒ t = 4 seconds.

∴ Time taken to reach highest point = 4 seconds.