Calculating Time Interval for Ball to Strike Ground | Ball Velocity Question

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Homework Help Overview

The problem involves calculating the time interval for a ball thrown downward from a height of 30.8 m with an initial speed of 7.75 m/s. The context is within the subject area of kinematics, specifically focusing on motion under constant acceleration due to gravity.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the initial speed of the ball and the acceleration due to gravity, questioning the neglect of the initial speed in the calculations. There is an exploration of the appropriate kinematic equations that could be applied to the scenario.

Discussion Status

Some participants have provided hints regarding the use of constant acceleration equations, while others are clarifying their understanding of the problem setup. There is an acknowledgment of the need for further exploration of the correct approach to the problem.

Contextual Notes

One participant notes a lack of familiarity with kinematic equations, which may be impacting their ability to solve the problem effectively. Additionally, there is a mention of the problem being from a mechanics course, suggesting a potential gap in the necessary background knowledge.

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Homework Statement


A ball is thrown directly downward, with an initial speed of 7.75 m/s, from a height of 30.8 m. After what time interval does the ball strike the ground?




The Attempt at a Solution


The way I understand it is that since it is freefalling, it is moving at 9.8m/s towards that ground, thereby I neglected the 7.75m and did 30.8/9.8 = 3.14s..however it is wrong and the similar problem book is even numbered therefore cannot work through it backwards.. Any help?
 
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I am a Newbie said:

The Attempt at a Solution


The way I understand it is that since it is freefalling, it is moving at 9.8m/s towards that ground, thereby I neglected the 7.75m and did 30.8/9.8 = 3.14s..however it is wrong and the similar problem book is even numbered therefore cannot work through it backwards.. Any help?
I'm afraid that is incorrect; the ball is accelerating at 9.81m/s2 which makes a big difference. I'm assuming that your doing a mechanics course, so which kinematic equations do you know?
 
Actually just in a standard Calc based physics, thereby I have no equations
 
Hint: The ball is moving at a constant acceleration.

You should have plenty of constant acceleration equations in a Calculus based Physics course to relate velocity, displacement, acceleration, and time.

If not, check out these...

http://hyperphysics.phy-astr.gsu.edu/hbase/mot.html

CS
 

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