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Ella throws a hockey puck up at a rate of 20 ft/sec from a height of 5 feet.
How long will it take for the hockey puck to hit her on the head if Ella is 5.5 ft tall?
I solved it and got 0.026 and 1.23 as the answers (rounded), but I don't know which one is the correct answer.
Also I used the equation h=-0.5a^2 + vt + s. a is 32.
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The equation you used looks strange.
The standard and canonical equation to be used in such problems, is h = -0.5a*t^2 + vt + s with a = 32 m/s^2.
With the numbers, the equation to find the flight time (= "how long will it take") is
-16t^2 + 20t + 5 = 5.5,
or
16t^2 - 20t + 0.5 = 0
for simplicity.
Its solution is
= = = .
Of the two roots, you select the greater one (because the smaller time is for ASCENDING BRANCH)
t = = 1.225 seconds.
ANSWER. It will take 1.225 seconds to hit her on the head.
Solved and carefully explained.
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In this site, there is a bunch of lessons on a projectile thrown/shot/launched vertically up
- Introductory lesson on a projectile thrown-shot-launched vertically up
- Problem on a projectile moving vertically up and down
- Problem on an arrow shot vertically upward
- Problem on a ball thrown vertically up from the top of a tower
- Problem on a toy rocket launched vertically up from a tall platform
Consider these lessons as your textbook, handbook, tutorials and (free of charge) home teacher.
Read them attentively and learn how to solve this type of problems once and for all.
Also, you have this free of charge online textbook in ALGEBRA-I in this site
- ALGEBRA-I - YOUR ONLINE TEXTBOOK.
The referred lessons are the part of this textbook under the topic "Projectiles launched/thrown and moving vertically up and dawn".
Save the link to this online textbook together with its description
Free of charge online textbook in ALGEBRA-I
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson
to your archive and use it when it is needed.