The average person passes out at an acceleration of 7g (that is, seven times the gravitational acceleration on Earth). Suppose a car is designed to accelerate at this rate. How much time (in seconds) would be required for the car to accelerate from rest to 56.3 miles per hour?

I think the Fluther policy is not to help students with their homework, but I always hate this kind of problem and it seems to me that the g is just in there to provide some background and to confuse you.

7g=7*g=7*9.8m/s^2

It’s not graded, I’m doing extra work on my own and this one has stumped me for the past half hour. I know I’m probably over complicating it and that I’m going to feel like an idiot when I figure out how to do it (in that it took that long ;) )

@quarkquarkquark I’ve seen others get help with homework. Help the guy out :)

@barumonkey hah that helps a ton, thanks!

@quarkquarkquark thanks, but “help the girl out” :)

my bad

@katob3 are you planning to drive this car?

42

0.838 seconds

56.3 mph = 78.61 ft per second

1 g = 16 ft sec^2
7 g = 112 ft sec^2

112 ^ .838 = 78.65 ft per second

a=(Vf-Vi)/t

7*9.8m/s^2=(56.3m/h-0mi/h)/t

From there it’s just algebra and arithmetic (with conversion factors)

@eponymoushipster How did you get this? I keep getting 11 seconds, but that can’t be right

@katob3 simple. i googled it

I worked it out to 0.36 seconds (given 3600s/h and 1609m/mile as conversion factors).

^ ha

Well apparently neither 42 nor 11 is right (but I’m still getting 11?)

68.6m/s^2 = (754.88 m/s – 0m/s)/(t)

no, 42 is definitely the answer.

@eponymoushipster lol people need to follow links.

(56.3mi/h) * (1h/3600s) * (1609m/mile) = 25.16m/s (not 754.88)

@ABoyNamedBoobs03 most definitely.

Nope, Barumonkey got it, it was .36 seconds (it’s an online textbook so it marked it wrong when I put 42)

@barumonkey THANK YOU!!!

I figured out where I got the 754.88 though (trying to take a short cut while converting the long way)—->

(56.3mi/hr)(1hr/60min)(1min/60s)*(1609m/1mi) ——I multiplied all the top numbers and tried to divide by 120, instead of dividing by 60 2x

Full solution:

Vf = Vi + at;
Vf = 25.17, Vi = 0, a = 7g;
25.17 = 7gt;
t = 25.17/(7*9.81) = 0.3665s

Ah why am I seeing imperial units on a page about physics?!?!

@doggywuv lol

T_T I hate math….

Where do i get this car?

This has mostly already been solved it looks like, but I’m going to throw in my two cents anyway.

For the original question, the g is necessary there. It tells you what acceleration the car achieves. so, it’s 7*g, where g is 32.174 ft/s^2, 1 ft = .00019 mi, so g = .006 mi/s^2, and 7g is .042 mi/s^2

now, we just need 56.3 miles per hour = 0.016 miles per second (just googled that, didn’t feel like doing it by hand), and so (.016 mi/s)/(.042 mi/s^2)= .38 s

(I rounded a bit more then you did, probably, hence the .02s difference)