# An inclined planeUP or DOWN?

1. Jul 21, 2006

### alwysnforevr002

Okay let me start over. This question is confuzing me.
If i can figure out what it means than i already know the answer. I am simply looking for a further explanation. Basically the question is

The motion of a ball on an inclined plane is described by the equation DeltaX = 1/2(acceleration(delta t)(squared))
Which of the following quantities must have a value of zero?
xi
xf
vi
tf

NOW, my problem is that i dont know if the "inclined plane" is a plane starting from the top and then going down or starting from the bottom and going up.

I hope that is bit more clear. i apologize for the mess

2. Jul 21, 2006

### Andrew Mason

You are supposed to answer that question from the equation of motion:

$$\Delta x = \frac{1}{2}at^2$$

Start by determining what a is. What forces are acting on the block? If the net force constant? How does this affect the block's motion? What is the general equation of motion of this kind of force in terms of the distance moved? (hint: it includes all the variables listed). What must those variables be if the given equation is correct?

AM

3. Jul 21, 2006

### alwysnforevr002

I think the correct answer is the intial velocity. because if it started at the top of the plane at rest and rolled down the initial velocity would be zero.

4. Jul 22, 2006

### Andrew Mason

That is the right choice but the wrong answer. The question does not say that it started at rest. You have to figure that out.

For an object undergoing constant acceleration, a, what is the general equation of motion as a function of time t in terms of a, t, xi and vi? (assume, xi, vi are not 0. How do they affect the determination of x?);

AM