Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

Answer: $a=v^2/d$ is the formula I needed.

This is a problem in a programming assignment, I haven't taken physics.

I have a starting speed (0 m/s), an final speed (208.33m/s) and the distance it took to reach that speed (200km). I need to get the time it will take to travel any arbitrary distance lower than 200km.

From what I remember in highschool, I used basic calculus to get $a/2(t^2)=distance$ or for what I have $t=\sqrt(400000(m/s)/a)$. what I don't know is the acceleration, usually to calculate acceleration I'd need time. I'm not sure where to go from here.

share|improve this question

closed as off-topic by Dimensio1n0, John Rennie, tpg2114, Michael Brown, Qmechanic Nov 2 '13 at 12:12

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – Dimensio1n0, John Rennie, tpg2114, Michael Brown, Qmechanic
If this question can be reworded to fit the rules in the help center, please edit the question.

    
Is the acceleration constant throughout the time interval in which the speed increases? –  GTX OC Oct 4 '13 at 5:08
    
Yes. I already have the answer though. Thanks for suggesting the edit. –  Dan Oct 4 '13 at 5:09
    
The "formula I needed" is not correct... –  User58220 Oct 4 '13 at 6:29
    
Oh well, the assignment was due before your post. It's not a big grading factor, I'm not sure anyone got that part right. –  Dan Oct 7 '13 at 5:49

2 Answers 2

Converting all units to SI: $$u=0$$ $$v = 208.33 \text{ m/s}$$ $$d =200000\text{ m}$$So: $$a=\frac{v^2-u^2}{2d}=0.1085\text{ m/s}^2$$

Then, for any distance,$d$ in meters:$$t=\sqrt{\frac{2d}{a}}$$This vehicle maintains a feeble, but constant, $0.01\text{ g}$ for a $200\text{ km}$ trip lasting a little more than 30 minutes.

share|improve this answer

According to the question while the car travels from 0 to 200 m/s with constant acceleration it covers a total distance of 200km.

Applying the formula
$$2as=v^2-u^2$$
where v is the final speed,u is the initial speed and s is the distance. Here u=0m/s,v=208.3m/s and s=200km.
Putting the values we get
$$a=0.1085034 m/s$$

Finally using $$s=ut+1/2at^2$$ where s is the distance covered, u is the initial velocity,a is the acceleration and t is the time, we get the distance(in m) covered at any time t(in seconds).

Here u=0m/s. We get $s=1/2at^2$. Given any s<200km you can now find the time it takes to cover that distance.

share|improve this answer
    
Wouldn't it be 0.1085 since 2*200km is at the bottom, not 2*200m? –  Dan Oct 4 '13 at 5:42
    
This answer seems to use $\frac{km}{hr^2}$ as its unit for acceleration... –  User58220 Oct 4 '13 at 6:07
    
@Dan: yeah you are correct. I took the speeds in km/h. –  GTX OC Oct 4 '13 at 6:21

Not the answer you're looking for? Browse other questions tagged or ask your own question.