How to find distance with the given information?

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SUMMARY

The discussion focuses on calculating whether a car traveling at 40 km/hr can stop before hitting a child 13 meters ahead, given a deceleration of 8.0 m/s² and a reaction time of 0.25 seconds. The key steps involve breaking the scenario into time intervals where acceleration is constant, calculating displacement for each interval, and comparing the total displacement to the distance to the child. The conclusion is that by applying the appropriate kinematic equations for each phase of the motion, one can determine if the car stops in time.

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  • Understanding of kinematic equations for constant acceleration
  • Basic knowledge of physics concepts such as speed, distance, and deceleration
  • Ability to perform calculations involving time, distance, and acceleration
  • Familiarity with units of measurement (e.g., meters, seconds)
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  • Study the kinematic equations for uniformly accelerated motion
  • Learn how to calculate displacement during different phases of motion
  • Explore the concept of reaction time and its impact on stopping distance
  • Investigate real-world applications of these calculations in traffic safety
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Students studying physics, drivers interested in understanding stopping distances, and traffic safety professionals analyzing vehicle response times.

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The speed limit in a school zone is 40 km/hr. A driver traveling at this speed sees a child run into the road 13 m ahead of the car. He put on his breaks and decelerates at a rate of 8.0 m/s^2. If the drivers reaction time is .25 s, will the car stop before hitting the child?



a= - 8.0 m/s^2
t= .25s
d= ?

I am just confused about what equation to use.
 
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There isn't an equation per se because many things happen. The equations can only be used when acceleration is constant. You will use one equation for each time period in which the acceleration is constant.

The way to do it is to write down the important points in time (so that the periods between those points have constant acceleration), then calculate displacement and time for each point. By the end, you will have the final displacement and you can check whether it is <= 13m.
 

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