Vertical throw initial height 15 time 3s until hiting ground

AI Thread Summary
To determine the initial speed of a ball thrown vertically from a height of 15 meters, the equations of motion are applied, specifically d = v_initial*t - 0.5*g*t^2 and v = v_initial + g*t. The ball takes 3 seconds to hit the ground, indicating that it reaches its maximum height before descending. To find the initial speed, one must solve the quadratic equation derived from these formulas. Additionally, the time at which the ball returns to the 15-meter height can be calculated using the same equations. Understanding quadratic equations is crucial for solving these types of problems effectively.
Justas
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Homework Statement


Height - 15m
Time when ball hits the ground after upward throw 3 s.

I have been trying to find intitial speed with these formulas :
d=v_initial*t-0.5*g*t^2
and
v=v_initial+g*t

Please help to understand how to find initial speed and after what time the ball is at 15m height again.
 
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Justas said:

Homework Statement


Height - 15m
Time when ball hits the ground after upward throw 3 s.

I have been trying to find intitial speed with these formulas :
d=v_initial*t-0.5*g*t^2
and
v=v_initial+g*t

Please help to understand how to find initial speed and after what time the ball is at 15m height again.

You need to post what you've done. Hint: what do you know about quadratic equations?
 

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