# Rollercoaster& velocity problem Please Help

1. Mar 19, 2006

### chazgurl4life

Suppose the roller coaster in Fig. 6-41 (h1 = 38 m, h2 = 12 m, h3 = 20) passes point 1 with a speed of 1.40 m/s. If the average force of friction is equal to one third of its weight, with what speed will it reach point 2? The distance traveled is 35.0 m.
m/s

Please view atachment

I dont even know where to start with this problem

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2. Mar 19, 2006

### Hootenanny

Staff Emeritus
I'm afraid you problem isn't going to get answered ASAP, it takes a while for attachments to be approved. Perhaps if you described your problem?

3. Mar 19, 2006

### PPonte

4. Mar 19, 2006

### chazgurl4life

ok so there is a rollercoaster on the ramp and there are 3 diffeternt positions allocated (hi= 38m, H2=12m, H3=20m). Now according to the problem there is a friction force on the rollercoaster which amount to 1/3 of thr rollercoaster's weight. But they dont give the weight of the rollercoaster. Since there is a long distance between hi and h2 they want to know whats the velocity at point 2 ( which is btween H1 &2). My porblem is that i dont even know what equations i should be using because my prof always gave us similar problems in which mass was given. is so i would use :

mgd=mgd2 + friction(distance)

5. Mar 19, 2006

### Hootenanny

Staff Emeritus
That is the correct equation to use. Think about how else you could write the frictional force. What other equations do you know for friction?

6. Mar 19, 2006

### chazgurl4life

force of friction = coefficient of friction X normal force
coefficient of friction mass(9.8)
Force of Friction= coefficient of friction x mgcostheta
with the other equation : friction =mgd/mgd2
-----------
distance

7. Mar 19, 2006

### Hootenanny

Staff Emeritus
$$F_{friction} = \mu R = \mu mg$$

Substitute $F_{friction} = \mu mg$ into your equation and you will find that the masses cancel...

8. Mar 19, 2006

### chazgurl4life

umg=mgd/mgd2
u=d/d2

9. Mar 19, 2006

### PPonte

chazgurl4life,

I think you did a mistake:

umg=mgd/mgd2
um = d/d2

Only the masses in bold cancel and g.

10. Mar 19, 2006

### chazgurl4life

oh ok thanx

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