# Homework Help: Ramp: Forces and Motion Investigation Lab

1. Feb 14, 2012

### Asuncion

1. The problem statement, all variables and given/known data

We are to use the Ramp: Forces and Motion simulator located at http://phet.colorado.edu/en/simulation/ramp-forces-and-motion.

First part we are to chose 2 objects. I chose the small crate and textbook and then slide then down a ramp at 30 degree angle. Using the following parameters:

μs=0.5
μk=0.3
g=9.8m/s^2 Earth
brick wall
wood friction

Hypothesis 1: If the mass of an object (blank), then the distance it slides from the end of the ramp will (blank) because........

After completed the simulation the 10 kg textbook and the 100kg small crate both go the same amount of distance.

Hypothesis #2: If the angle of the ramp(blank), then the distance it slides off the end of the ramp will (blank) because.........

In this experiment I used the same object (10kg textbook), at different angles ( 30 and 45 degrees). The book moved further when ramp was at 45 degree angle than 30 degree angle.

2. Relevant equations

1. How do I state the hypothesis 1 and hypothesis 2: Knowing that acceleration is inversely proportational to the mass, which has nothing to do with the distance traveled, I think.

2. Next I am to graph using the independent and dependent variables? Not sure which is which. I do know that the dependent variable is the y-axis and independent variable is the x-axis.

3. Then I am to derive a general formula relating the objects mass (m) and the distance it slide.

And a formula for relating the angle and the distance it slides.

Hope I didn't overwhelm you.

3. The attempt at a solution

So here's what I know.
a=acceleration
F(net)= net force
m=mass
F(grav)=gravity force
F(fric)= friction force not sure if I should add the two friction forces together of which one to chose and use)
cos=cosine

a=F(net)/m
F(net)= F(grav)+F(fric)+F(norm)
F(norm)=m*g*cosθ
F(fric)=μ* F(norm) not sure which coefficient to use the kinetic friction or static friction.

Don't know where to began. thank you for your attempt to help me.

2. Feb 14, 2012

### Shootertrex

First, your $F_{net}$ equation is incorrect. It should look something like this:

$F_{net}=F_{gravity}+F_{normal}-F_{friction}$

Friction pulls the objects up the ramp while gravity pulls them down. You have friction pushing in the same direction as the resultant of gravity and normal force. While I mention the resultant, you did not include the formula for this. When gravity and normal force are added together, it will make the formula simpler. When you solve for acceleration using a $F_{net}$ equation that includes the resultant, I think you will find the answer to Hypothesis #1.
For Hypothesis #2, you will need to look at how the forces are affected by sine and cosine as the angle increases/decreases.
For your graph, the independent variable is the variable that you are changing, and the dependent variable is the variable that is affected due to the independent being changed. I hope that made sense.

3. Feb 15, 2012

### Asuncion

Which coefficient do I use to get force friction, static or kinetic?

4. Feb 15, 2012

### Shootertrex

Static friction would be used to see if the object would move down the ramp at that angle. Kinetic friction would be used as the opposing force pushing the object back as it moved. Since in all the trials you listed the object moved, what do you think? (hint: it's kinetic)

5. Feb 15, 2012

### Asuncion

Okay, great so I use the kinetic friction coefficient because the object moved, got you. Now....

6. Feb 15, 2012

### Asuncion

Confused why is the y axis of the corrdinate system tilted to the right instead tilting it to the left?

7. Feb 15, 2012

### Asuncion

Disregard last question.. my bad

8. Feb 20, 2012

### Asuncion

Thanks shootertrex for the help!

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook