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Q & A: Can a car accelerate to 150 mph in a city block?

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Most recent answer: 07/21/2015
Q:
This is a bar room question. I have overhead some one claim that they have a car that will accelerate from 0 to 150mph and then decelerate to 0 in the distance of a city block. With 40 years and two beers between me and my last physics class, I do a quick head experiment and determine that this is B.S., But the beer, time and patience to calculate the G forces involved (will the driver pass out?) and to determine if the tires will maintain a no slip contact with the road cause the solution to to elude me. I think that knowing the staring and ending velocities and assuming constant acceleration this has enuff known variables to calculate the answer. Assume the tires are Michelin All Weather MX and the car is a 1967 Dodge 440 Police Interceptor, which can only accelerate in a straight line. Calculate the probability that this assertion is Bull S---. You can substitute a 1965 Ferrari 330 GT 2+2 Coupe for the Dodge if you are Italian, but you still must assume straight line acceleration.
- Bill Barnes (age 67)
Anchorage Alaska
A:

I don't know how long it takes a 1967 Dodge Polara 440 to accelerate to 150 mph, and I couldn't find an answer online. (Can it even go that fast? Shows what I know about cars...)

Let's consider a new car with better performance. A 2015 Porsche 918 Spyder is supposed to be able to reach 150 mph in 12.8 seconds (based on a fit to ). An important thing to note is that it does not have constant acceleration up to 150 mph, but let's assume it does to make our estimate easier. (The acceleration actually decreases at higher speeds, so we're going to underestimate the distance... if it's still longer than a city block, we'll at least know that your story is impossible.)

 We can use the to caluclate how far the car travels during the 12.8 seconds it takes to get to 150 mph. Using the first equation from that page:

distance = (average velocity) × (time) = (initial velocity + final velocity)/2 × (time) = (0 m/s + 67 m/s)/2 × 12.8 s = 428 meters

(150 mph = 67 m/s). So, it will take at least 428 meters just to accelerate up to 150 mph. That's almost twice the length of a standard city block (274 meters), so I agree that "this assertion is Bull S---" even without worrying about stopping distance.

Rebecca H.


(published on 07/21/2015)

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