Calculating Freefall Time: How Long Will the Book Take to Hit the Ground?

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    Grade 11 Gravity
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Homework Help Overview

The discussion revolves around calculating the time it takes for objects to fall under the influence of gravity, specifically focusing on scenarios involving a textbook dropped from a hot air balloon, a pop fly, and a ball thrown on the moon. The subject area includes kinematics and gravitational effects.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the time it takes for a textbook to hit the ground when dropped from a height, questioning the simplicity of the calculations. There are attempts to apply basic kinematic equations and considerations of initial velocity and gravitational acceleration in different contexts.

Discussion Status

Some participants express confusion about the calculations and the assumptions made regarding gravitational acceleration. There is a suggestion to utilize kinematic equations for a more thorough analysis, indicating a productive direction in the discussion.

Contextual Notes

Participants are navigating through multiple related problems, indicating a potential lack of clarity in the application of physics concepts. There is also a mention of the importance of demonstrating initial attempts to facilitate assistance.

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Questions;

1)A person in a hot air balloon at 500m is rising at 20m/s.
In order to rise up even faster, she drops her physics textbook out of the balloon.
How long will the book take to hit the ground?

Since it's thrown at 500m high, and Gravity is -9.8m/s
500/9.8 = 51 seconds
However I'm not pleased with the answer, I just feel something is missing and it should not be that easy.

2)A pop fly rises 80m after being hit by a bat.
How long is it in the hair before it is caught by the catcher?

Same logic.
80/9.8 = 8.1 seconds.

3)A ball is thrown up with a Vi of 30m/s^2 on the moon where gravity is 1/6g
How high?
How long total?
How long until ball is 100m high?

Moon gravity = 1.6

How high?
30/1.6 = 18.8s
1.6*18.8 = 30
30*18.8 = 564
564 - 30 = 534m

How long total?
30/1.6 = 18.8sHi there, I'm new to these forum, and new to physics!
These are some of the question that are given to me (There lots more!). But basically they're of the same concept so helping me with 3 of these will probably make me understand the rest of the question I'm given.

Thanks for the help!
 
Last edited:
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Welcome to the forum! I'm new too. =]
Just know that you'll get help much faster if you show that you tried the problem first

Edit: You should read this https://www.physicsforums.com/showthread.php?t=94379"
 
Last edited by a moderator:
I've tried the question and I'm really confused right now!
I didn't type it out because it's a mess in my book.
Thanks!
 
Fritsc said:
Questions;

1)A person in a hot air balloon at 500m is rising at 20m/s.
In order to rise up even faster, she drops her physics textbook out of the balloon.
How long will the book take to hit the ground?

Since it's thrown at 500m high, and Gravity is -9.8m/s
500/9.8 = 51 seconds
However I'm not pleased with the answer, I just feel something is missing and it should not be that easy.

Welcome to PF :smile:

No, the acceleration due to gravity IS NOT -9.8 m/s, it is -9.8 m/s2

How about using the kinematic equations for motion with constant acceleration here?
 

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