Why Is My Calculation of Acceleration Marked Wrong?

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Homework Help Overview

The discussion revolves around a freshman physics problem involving the calculation of acceleration for a block being pulled across a rough surface. The original poster presents a scenario where a force of 22.5 Newtons is applied to a 4 kg block moving at a constant velocity, leading to a question about the acceleration when the force is removed.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to apply the formula for acceleration, questioning their calculation based on the force and mass provided. Some participants question the direction of the force relative to the block's velocity, suggesting a reconsideration of the original calculation.

Discussion Status

The discussion is active, with participants engaging in clarifying the assumptions behind the calculation. A hint has been provided regarding the direction of the force, and the original poster expresses a realization about the sign of the acceleration. There is also mention of the original poster figuring out a subsequent question independently.

Contextual Notes

The problem involves understanding the dynamics of motion and the effects of forces, particularly in the context of constant velocity and the implications of breaking the pulling force. The original poster's confusion highlights the importance of considering direction in physics calculations.

oooo
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Here is a problem from our freshman physics homework--it seemed pretty simple and self-explanatory:
(refering to a diagram) 22.5 Newtons of force must be used to pull the 4 kg block across the rough surface at a constant velocity of 6.7 m/sec to the right. If the string pulling the block rightward were to break, what would be...
(a) the acceleration of the block:
Now, isn't the formula for acceleration a=F/m?
Wouldn't a = 22.5N/4kg = 5.625 m/s^2? It seems simple enough, yet it is marked wrong. If I made a silly mistake, I would like to know why, because it seems really easy and I don't know where I went wrong.
THEN, after that, it prompts me to find the time it would take for the block to stop. Not quite sure how to figure that out... any suggestions?
 
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oooo said:
Wouldn't a = 22.5N/4kg = 5.625 m/s^2?

Nope. What is the direction of the force acting relative to the velocity of the block?
HINT: You are very close.

~H
 
Last edited:
ooh, so it is -5.625! Thanks!
OH! and about my time question, I thought about it some more and I figured it out (no need to help) but thanks though!
 
oooo said:
ooh, so it is -5.625! Thanks!

My pleasure.

~H
 

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