Question

A boy throws a rock straight up into the air. It reaches the highest point of its flight after 2.5 seconds. How fast was the rock going when it left the boy's hand?

Answer 1

9.8 m/s^2 and its because thats the earth gravity unless the composition of the earth is change. hope this helps

Answer 2

`v_i = 24.52 m/s`

Step-by-step explanation:

As we know that when rock moves upwards against gravity the velocity of rock will decrease with time and when it will reach the highest point it's velocity becomes zero

So we can use kinematics equation here such that

`v_f = 0`

`v_i = ?`

`a = -9.81 m/s^2`

`t = 2.5 s`

now we will have

`v_f - v_i = at`

`0 - v_i = (-9.81)(2.5)`

`v_i = 24.52 m/s`