# Homework Help: Constant Breaking force for roller coaster

1. May 27, 2014

### rexorsist

I really don't understand this:

Consider a frictionless, 12000-kg roller coaster that starts at rest at the top of a hill, point A, 95 m high. It goes all the way the 75 degree steep hill and coasts horizontally (for an unspecified distance) before reaching point B (0 m high). The entire ride lasts 10 seconds and breaks engage with a constant force during last 4 seconds. Calculate:

a) the constant breaking force that must be applied to bring the roller coaster to a stop at point B.

b) the work being done by breaks to bring the roller coaster to a stop at point B.

I don't understand the question at all. The wording is weird. How would I start this? I have no clue what so ever.

2. May 27, 2014

### SammyS

Staff Emeritus
Except for the misspelling of "brakes" and "braking", the description is quite clear.

Conservation of Energy?

Work?

Newton's 2nd law?

Kinematic equations?

etc.

3. May 27, 2014

### rexorsist

Yup, I know those equations.

I know that first we're going to figure out the distance down the slope. I used the sin law to figure out the length. Then I'm going to use the first kinematic equations (V2=V1+AxT , where V2 equals final velocity, V1 equals initial velocity, A equals acceleration, T equals time). Once I solve for acceleration, I would then use the Force = Mass x Acceleration formula to solve for the force required for the break.

Would I be able to find the correct answer using this method?

Thank you so much for your help!

4. May 27, 2014

### SammyS

Staff Emeritus
You should be able to use Conservation of Energy to find the speed of the roller coaster at the bottom of the hill, before braking.

5. May 27, 2014

### rexorsist

How would I use the Conservation of Energy formula?

If the equation is ET=1/2(mass)(Velocity squared) + (mass)(gravity)(height)

Would I assume height to be zero? Or would it be 95m?

EDIT: I know I would isolate Velocity Squared.

Last edited: May 27, 2014
6. May 27, 2014

### rexorsist

Please someone! I need urgent help. I need to know how to do this before tomorrow. I am begging.

7. May 28, 2014

### tms

You look at the total energy at the top and at the bottom of the slope.

8. May 28, 2014

### SammyS

Staff Emeritus
There is a starting height and an ending height.

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