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A mate is making a toy car for a schools competition, it has to travel 12m on a flat track, and is powered by a small gas canister that is given to them at the start of the race.
Last year they did the 12ms in 0.8s (record is 0.62s).
Question is - What kind of G's are put on the car during acceleration and deceleration? Assuming that the car is stopping in a cushion over about 30cm. Rough answer is fine...
Cheers
approx mass of the car etc?
it'll be massive, over 50g on acceleration I'd think
Going by 12 meters in 0.62 seconds..
Average speed = 12 / 0.62 = 19.35 meters per second.
Assuming you start from 0 meters per second, and assuming linear acceleration (unrealistic, will come it in a bit), then you must accelerate up to 19.35 x 2 = 38.7 meters per second.
Accelerating up to 38.7 meters per second in 0.62 seconds, 38.7 / 0.62, gives you an acceleration of 62.41 meters per second per second.
However, it's much more likely the acceleration will be higher just after the start, and will drop off towards the end, so this is, if you like, somewhat of a lower bound.
62.41 / 9.81 = 6.36 G during acceleration.
Deceleration from 38.7 meters per second over 0.3 meters, again, we're decelerating to 0 meters per second, so assuming linear deceleration we will have an average speed of 19.35 meters per second again.
Covering 0.3 meters at an average of 19.35 meters per second will take 0.3 / 19.35 = 0.016 seconds.
Decelerating from 38.7 meters per second in 0.016 seconds will be a deceleration of 38.7 / 0.016 = 2418.75 meters per second per second.
2418.75 / 9.81 = 246.6 G during deceleration.
I think that's all roughly right, it's been a long time since I've done this sort of thing. Assuming linear acceleration does generally give you a lower bound on these things though, so the actual G force could be much higher.
For comparison, say you drive a car into a brick wall (silly, I know) at 40mph, and the front end of the car crumples inwards by 1 meter (hence giving you a stopping distance of 1 meter from 40mph).
That should give you about 16.5 G. Which would hurt.
F1 in Schools competition?
Uniform acceleration starting from rest covering 12m in 0.62 seconds gives an acceleration of 62 m/s^2. Thats using s=ut+1/2at^2
Final speed is .62*62= 37 m/s (just over 80mph)
deceleration using v^2=u^2+2as is 2280 m/s^2. 226 g
Nice to be able to agree with real man
Realman - after reading that I am now nursing a semi!
I wonder if there are some interesting measurements to make using a smartphone similar to this:
Realman - after reading that I am now nursing a semi!
Well it's good to hear someone appreciated it, I totally let myself get nerd sniped and was nearly late for the club ride..