Is My Calculation for Car Deceleration Speed Correct?

AI Thread Summary
The calculation for car deceleration from 100 km/h over a braking distance of 45.73 m uses the formula v^2 = u^2 + 2as, rearranged to a = (v^2 - u^2)/2s. The user converted 100 km/h to approximately 27 m/s and calculated a deceleration of -7.97 m/s². A response confirmed the calculation was correct but noted that the initial speed conversion could be more precise. Additionally, it was mentioned that real-world deceleration is not constant, as it typically increases as speed decreases.
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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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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