Find the height from which the ball was thrown

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Homework Help Overview

The problem involves a ball being thrown from a building with an initial velocity at an angle below the horizontal, and the goal is to determine the height from which it was thrown. The context is kinematics, specifically projectile motion, with a focus on vertical motion under gravity.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the application of kinematic equations and the correct interpretation of initial velocity components. There is a focus on the sign conventions used for the vertical component of the velocity and gravity.

Discussion Status

Some participants have provided feedback on the original poster's approach, questioning the sign of the initial vertical velocity and suggesting the need for consistency in defining directions. The discussion is ongoing, with attempts to clarify the setup and assumptions involved.

Contextual Notes

There are indications of confusion regarding the signs used in the equations, particularly in relation to the direction of the initial velocity and gravitational force. The original poster's calculations have been challenged, but no definitive resolution has been reached.

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Homework Statement


A ball is tossed from an upper-story window of a building. The ball is given an initial velocity of 9.00 m/s at an angle of 16.0° below the horizontal. It strikes the ground 5.00 s later. (Ignore air resistance.)
(b) Find the height from which the ball was thrown.

Homework Equations



Y-Yo= Vyot -1/2gt^2

The Attempt at a Solution



Yo= -Vyot +1/2gt^2

Yo= -(9sin16)(5) + 1/2(9.8)(25) = 110m
but the answer is wrong.
 
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Consider the sign of vyo.

ehild
 
xjasonx1 said:

Homework Statement


A ball is tossed from an upper-story window of a building. The ball is given an initial velocity of 9.00 m/s at an angle of 16.0° below the horizontal. It strikes the ground 5.00 s later. (Ignore air resistance.)
(b) Find the height from which the ball was thrown.

Homework Equations



Y-Yo= Vyot -1/2gt^2

The Attempt at a Solution



Yo= -Vyot +1/2gt^2

Yo= -(9sin16)(5) + 1/2(9.8)(25) = 110m
Your formula above is incorrect. The ball is tossed out of the window at a downward angle. This means that the vertical component of the velocity is in the same direction as gravity is acting. In your formula, Vy0 is negative, but the gravitational force is positive. You can define which sign corresponds to up or down, but you have to be consistent.
xjasonx1 said:
but the answer is wrong.
 
Thank you!
 

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