Motion, Finding stopping distance

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Homework Help Overview

The discussion revolves around a physics problem related to motion, specifically calculating the stopping distance of a minibus when the driver applies brakes. The scenario involves a mass of 1.5*10^3 kg, an initial speed of 30 m/s, and a braking force of 9*10^3 N.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to calculate the stopping distance using basic equations of motion but questions the discrepancy between their result and the textbook answer. Some participants suggest using different equations suited for constant acceleration and clarify the meaning of variables in those equations.

Discussion Status

The discussion is ongoing, with participants exploring different equations and clarifying terminology. Guidance has been offered regarding the appropriate equations to use for the scenario, and there is an acknowledgment of the need to determine the distance covered while stopping.

Contextual Notes

There is a mention of confusion regarding the initial position and the variables used in the equations, indicating a need for further clarification on these concepts. The original poster is working within the constraints of a homework assignment, which may impose specific methods or approaches to be used.

TheRedDevil18
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I just want to confirm if what I am doing is right, please correct me because my textbook gives me a different answer.

Homework Statement


The mass of a minibus with the driver is 1.5*10^3 kg. The driver is moving at a speed of 30m.s when he notices that the traffic lights ahead have turned red. He applies a force of 9*10^3 N on the brake pedal.

A) How far must he have been from the traffic lights if he were able to stop in time?


Homework Equations



a=Fnet/m
s=d/t

The Attempt at a Solution



a=9*10^3/1.5*10^3
= 6 m.s^-2

using the equation a=v/t i got a time of 5 seconds

so
d = s*t
= 30*5
= 150 m but my textbook says it is 75 m
 
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The equation you are using for distance only works for a constant speed.

Try other equations like:

d=d0 + v0t +1/2at^2

that are suited to constant acceleration.
 
doppelganger said:
The equation you are using for distance only works for a constant speed.

Try other equations like:

d=d0 + v0t +1/2at^2

that are suited to constant acceleration.

What is that 0 in the equation. Is it initial distance and final velocity?
 
TheRedDevil18 said:
What is that 0 in the equation. Is it initial distance and final velocity?
d0 is initial position.

v0 is initial velocity.
 
His initial velocity would be 30m.s but what is his initial position?
 
If you find out how much distance the driver covers as he stops, you will know the minimum distance that he must be from the light to stop in time.
 
Ok thanks, i will try it out
 

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