Calculate Distance for Bob to Stop at Stop Sign

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Homework Help Overview

The problem involves calculating the distance required for a car to come to a stop when brakes are applied, specifically focusing on uniform deceleration from an initial speed of 20.0 m/s to a complete stop over a time period of 4.0 seconds.

Discussion Character

  • Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the calculation of distance using different approaches, including average velocity and acceleration formulas. Some question the correctness of the initial distance calculation of 40 m.

Discussion Status

There appears to be agreement on the calculated distance of 40 m, with participants confirming the correctness of the approach used to derive this result. However, the discussion includes various methods of reaching this conclusion without a definitive consensus on a single method.

Contextual Notes

Participants reference specific values such as initial and final velocities, time, and acceleration, while exploring the implications of using average velocity in their calculations. There is an emphasis on ensuring the calculations align with the uniform deceleration context.

billybobay
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Homework Statement


When Bob applies the brakes to his car, it slows uniformly from 20.0 m/s to 0.0 m/s in 4.0 s. How many meters before a stop sign must he apply his brakes in order to stop at the sign?


80 m

60 m

40 m

20 m



Homework Equations



d=(20+0)/2(4)
d= 40 m

The Attempt at a Solution



Bob needs 40 m to stop his car.

Would that be correct?
 
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Yes.
 
Distance = ??
Time = 4s
Velocity initial = 20m/s
Velocity final = 0m/s
Acceleration = ??

A = Vf-Vi / T
A = -20 / 4
A = -5m/ss

D = ViT + ATT/2
D = (20)(4) + (-5)(4)(4) / 2
D = 80 + -40
D = 40m

yes, you're correct
 
@ billybobay,

It's perfectly fine to work it out the way you did, using average velocity.
 

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