Motion at constant acceleration

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SUMMARY

The discussion revolves around calculating the initial speed of a car before braking, given a skid mark length of 92 meters and a deceleration of 7.00 m/s². The correct approach utilizes the equation vf² - vi² = 2ad, leading to an initial speed (vi) of approximately 35.889 m/s. The initial incorrect assumption involved dividing distance by deceleration to find time, which is not a valid method for this scenario. The final solution confirms the use of kinematic equations for accurate results.

PREREQUISITES
  • Understanding of kinematic equations, specifically vf² - vi² = 2ad
  • Knowledge of basic physics concepts such as acceleration and deceleration
  • Familiarity with units of measurement in physics (meters, seconds)
  • Ability to manipulate algebraic equations
NEXT STEPS
  • Study the derivation and applications of kinematic equations in physics
  • Learn about the concepts of acceleration and deceleration in real-world scenarios
  • Explore problem-solving techniques for motion under constant acceleration
  • Practice additional physics problems involving initial and final velocities
USEFUL FOR

Students studying physics, particularly those focusing on mechanics, as well as educators looking for examples of kinematic equations in action.

steve snash
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Homework Statement


In coming to a stop, a car leaves skid marks 92m long on the highway. Assuming a deceleration of 7.00m/s^2 estimate the speed of the car just before braking.


Homework Equations



deceleration=7m/s^2, distance=92m

The Attempt at a Solution


I found there was not enough information to solve the problem, but i had a go, assuming dividing the distance by deceleration you would get time. 92/7 =13.14 seconds

I substituted this into the equation of motion x=x0+v0t+1/2at^2
=52.99m/s. Is this right??

NEED TO KNOW BY TOMORROW
 
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Why would distance divided by deceleration give you time? Why would x=x0+v0t+1/2at^2, which is an equation for displacement, give you speed?

Are you familiar with the equation vf^2-vi^2=2ad?
 
so the answer should be vi^2=2(7)(92)
=square root 1288=35.889 m/s??
 

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