Well, my first post here and it happens to be in the homework section. =P I finally escaped AP Chemistry (and got a 4 on my AP test!), but because I chose to take the AP Physics course for the upcoming school year, I undoubtedly have summer work. The task seemed simple enough: the teacher handed us a sheet of equations, and we locate them in the book; then we write down some information and provided an example problem.(adsbygoogle = window.adsbygoogle || []).push({});

Unfortunately, I have run into some obstacles.

On the equation, x = x0 + v0t + 1/2at^2, an equation of kinematics for constant acceleration, I am unsure about the answer to my example problem. It'd be wonderful if someone could flat-out tell me if my answer is correct or not, and it'd be even more wonderful if someone could point out where my mistake was.

Problem: A car is traveling at a constant speed of 27 m/s on a highway. At the instant this car passes an entrance ramp, a second car enters the highway from the ramp. The second car starts from rest and has a constant acceleration. What acceleration must it maintain, so that the two cars meet for the first time at the next exit, which is 1.8 km away?

Work: 27 m/s x 1/1800 m = 1/.015 s = 66.7 seconds.

First, Idivided(sorry!) the given speed and the distance to obtain the seconds.

x = x0 + v0t + 1/2at^2

(1800m)= (0) + (0) + 1/2a(66.7 s)^2

Then I plugged in the corresponding numbers.

a = .81 m/s^2

Finally, I solved for a.

I hope I did it right... I'm hesitant on whether I plugged the right things in. And I'm sort of hesitant on whether the equation is right for the problem. =\

Moving on... I located 78/80 of the equations needed (yay!), but the last two, I cannot seem to find anywhere. I googled it, I asked other people, but to no avail. So I'm wondering if anyone could identify it and simply provide me with the name of the equation.

One of the equations is U = -Gm1m2/r.

U being the potential energy, G being the universal gravitational constant, m1 and m2 being masses and r being radius or distance. I can't find it anywhere.

However, I found an equation similar to it: F = -Gm1m2/r^2. What is the difference between these two? Is there any difference at all?

The final equation I can't locate is: V = 1/(4 pi ε) Σ qi/ri.

ε, according to the key is emf, q is point charge and r is distance. I thought that it would be a series equation, but alas, it was nowhere to be found in that chapter.

I apologize for this post being so lengthy, but I hope that someone might be able to aid me in my work. [=

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# Homework Help: Equation of Kinematics for Constant Acceleration

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