# Acceleration, Solve for time (Algebra Based)

1. Sep 7, 2008

### Dig

1. The problem statement, all variables and given/known data
22. The average person passes out 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 would be
required for the car to accelerate from rest
to 60.0 miles per hour? (The car would need
rocket boosters!)

2. Relevant equations

3. The attempt at a solution
v1 = 60
v0 = 0
a = 7 * 9.8 => 68.6m/s^2

a = change in velocity/change in time

So, 68.6m/s^2 = 60mph/t
68.6 * t = 60mpg
t = 60/68.6
= 0.87 seconds

I am not sure if this is correct or not.
The answer seems within reason since a very high powered sports car accelerates from 0-60 miles per hour in around 3 seconds, so 0.87 seconds would line up well with the exaggeration of the speed of the car mentioned at the end of the word problem.

Any help is appreciated :).

2. Sep 7, 2008

### edziura

You are mixing English and SI units.

3. Sep 7, 2008

### Dig

Care to elaborate on where I went wrong and what I can do to correct my problem?

4. Sep 7, 2008

### lax1113

Dig.
What he/she meant was that you are using G's (or 9.8m/s2) which is the acceleration on earth in metric, and then Miles per hour, which is SI.

To fix this, take the MPH and multiply by .44 (or to be more exact, .44704) to get meters/second

By the way, the way to get the .44 is roughly 1600 meters/3600seconds = .44 (mile/hour hour=60 minutes=60 seconds. so 602)

This should give you some help, or at least point you in the correct direction.

Last edited: Sep 7, 2008
5. Sep 7, 2008

### Dig

Alright, if I multiply 60mi/h by .44, I receive 26.4m/s. I divide this by 68.6m/s^2 to get an answer of .385s? Both the numerator and denominator have 3 significant digits, so I stop at .385 correct?

I see my mistake now. Thank you both for pointing that out to me.

6. Sep 7, 2008

### lax1113

No problem Dig,
That seems correct to me.

Good luck in physics this year.

7. Sep 7, 2008

### Dig

Thank you so much :).