Question

Can someone explain please?​

Answer 1

Hi there!

We can begin by solving for the velocity in which the ball was thrown at using the following:

`v_f^2 = v_i^2 + 2ad`

At the top of the trajectory, the ball's velocity is equal to 0 m/s, so:

`0 = v_i^2 + 2ad\\\\vi^2 = 2ad \\\\`

'a' = acceleration due to gravity and 'd' is the max height, so:

`v_i^2 = 2(10)(5)\\\\v_i^2 = 10 m/s`

Now, we can use the same equation to calculate the final speed at 4.5 m. Remember, the acceleration is NEGATIVE in this instance (taking the negative direction to be in the direction of gravity).

`v_f^2 = 10^2 - 2(10)(4.5)`

`v_f^2 = 10^2 - 2(10)(4.5)\\\\v_f^2 = 100 - 90 \\\\v_f^2 = 10 \\\\v_f = \boxed{3.1 m/s}`