Question

A rock is thrown downward at a speed of 8.5 m/s and hits the ground 2.25 seconds later. From what height was the rock thrown? What was the velocity of the rock the moment it hit the ground?

Answer 1

Answer:

The velocity and height is 31 m/s and 44.4 m respectively .

Explanation:

Given :

Initial speed of rock , u = 8.5 m/s .

Time taken to reach ground , t = 2.25 s .

Also , acceleration due to gravity is , $g=10\ m/s^2$ .

Now , to find the velocity when it hit ground .

Applying equation of motion :

$v=u+at\\v=8.5+10\times 2.25\\v=31\ m/s$

Also , height from which rock is thrown is given by :

$h=ut+\dfrac{at^2}{2}\\\\h=8.5\times 2.25+\dfrac{10\times 2.25^2}{2}\\\\h=44.4\ m$

Hence , this is the required solution .