Is My Calculation for Car Deceleration Speed Correct?

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SUMMARY

The calculation for car deceleration speed when braking from 100 km/h over a distance of 45.73 meters is correctly approached using the formula v² = u² + 2as. The rearranged formula a = (v² - u²)/2s yields a deceleration of approximately -7.97 m/s² after converting 100 km/h to 27 m/s. However, the initial speed conversion should be more precise, as real-world deceleration is not constant and varies with speed reduction.

PREREQUISITES
  • Understanding of kinematic equations, specifically v² = u² + 2as
  • Ability to convert units from kilometers per hour to meters per second
  • Basic knowledge of acceleration and deceleration concepts
  • Familiarity with real-world vehicle dynamics and braking behavior
NEXT STEPS
  • Research advanced kinematic equations for variable acceleration
  • Learn about real-world factors affecting car deceleration rates
  • Explore vehicle dynamics simulations to visualize braking scenarios
  • Study the impact of tire friction and road conditions on braking performance
USEFUL FOR

Automotive engineers, physics students, and anyone interested in understanding vehicle braking dynamics and calculations related to deceleration.

nic_nic344
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Hey,
Just wanted to clarify that this was the right way to calculate the deceleration when braking from a speed of 100km/h when the braking distance of the car is 45.73m.

I am just using the formula v^2 = u^2 + 2as

Which i have rearranged to find a...

a = (v^2 - u^2)/2s ---------------- s = distance

And I converted the 100km/h to m/s
so...

a = (0 - 27^2) / 2 * 45.73
a = - 7.97ms/s

Is that right?

Or should I just leave the 100 in km...

and then by deceleration is like -100ms/s?

Thanks!
 
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Welcome to PF!

nic_nic344 said:
Hey,
Just wanted to clarify that this was the right way to calculate the deceleration when braking from a speed of 100km/h when the braking distance of the car is 45.73m.

I am just using the formula v^2 = u^2 + 2as

Which i have rearranged to find a...

a = (v^2 - u^2)/2s ---------------- s = distance

And I converted the 100km/h to m/s
so...

a = (0 - 27^2) / 2 * 45.73
a = - 7.97ms/s

Is that right?

Or should I just leave the 100 in km...

Hi nic_nic344! Welcome to PF! :smile:

Yes that's right … you get everything into the same units … except that your 27 isn't accurate enough. :wink:
 
Hey,
Yeh I will change the units to something like .78
Thanks for your help!
:)
 
real world the deceleration rate of a car is not steady state over the speed drop
it starts low and gets higher as speed drops
 

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