Question 802230: challenge questions
A stone is thrown vertically upwards, from the ground, with a velocity 49 m/s. After 2 seconds, another stone is thrown vertically upwards from the same place. If both the stone strike the ground at the same time, find the velocity, with which the second stone was thrown upwards.
Answer by KMST(5328)   (Show Source):
You can put this solution on YOUR website! The upwards velocity of each stone will decrease due to the acceleration of gravity, g, by 9.8 meter per second each second.
  (rounded)
The upwards velocity will reach zero and then become a negative number (meaning a downwards velocity) as the stone falls back to the ground.
 = the time of flight of the first stone (in seconds),
 = the time of flight of the first stone (in seconds),
 = height of either stone (in meters)
 = initial upwards velocity of the second stone (in m/s)
For the first stone, physics and math tell us that the height is
 or 
The first stone is on the ground when
 --> --> .
That means it is on the ground at the moment it "is thrown vertically upwards, from the ground," and it is on the ground 10 seconds later.
For the second stone, physics and math tell us that the height is
We want it to hit the ground  at  , just like the first stone, so
 --> --> -->
So  m/s (rounded because 9.8m/s^2 was a rounded number for g, 49m/s was given with only 2 significant digits, and I am in scientist mode now).
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