1. Jan 13, 2009

### amd123

I have a mid term tomorrow and I'm in a dire situation. I don't remember how to do kinematics equations like

A bus leaves the terminal and travels for 900s at an average velocity of 10 m/s before it stops at its first destination. How far from the terminal is the first destination?

The cars on a ride travel at a constant velocity of 4 m/s on a circular track that has radius of 4 m. What is the magnitude of centripetal acceleration?

A car traveling at 91 km/h approaches turn off for a restaurant 30 m ahead. If the driver slams onto the brakes with an acceleration of -6.40m/s^2 what will her stopping distance be?

Can someone please explain to me the basics and how to do these problems?

2. Jan 13, 2009

### Stovebolt

Are you permitted to have a list of kinematic equations? If so, things will be much easier.

A good way to approach these questions is to look at what values are given and what you want to find. This often will put you on the right track, even if you're not sure exactly how to get there. If you have a list of equations, try to select one that lists only one unknown variable.

For your first example, you are given a time (in seconds) and a velocity (in meters/second). You are then asked to find a distance. How would you go from (seconds) and (meters/second) to get an answer with units of distance only?

For your second example, you need to know the equation for centripetal acceleration (this happens to be a = v2/R).

For the third example, list all of your known variables and your unknown, paying close attention to units.

I hope this helps.

3. Jan 13, 2009

### amd123

yes we get a list of equations
We have not even discussed the 2nd question type so I was really confused and could you solve number 1 for me?
I also have projectile motion problems and ones that involve sin cos tan functions. I can do those but i needed to review the basic ones from earlier year

4. Jan 13, 2009

### Stovebolt

For the first example, think about it this way:

You want distance (meters). You have time (seconds) and velocity (meters/second). To find an answer that involves only meters, you multiply time by velocity:

(seconds) x (meters/second) = (meters)

Once you reach this point, you only need to substitute in the given values.

I'm not sure how much help I can give you with the 2nd type of question if you haven't covered that material. The best I can recommend is to find the equations relating to it and to try your best in applying them to a given problem. Focusing on the units may help in this case.

For projectile motion, I generally find the best approach for me is to look at each portion of the motion separately (vertical motion upwards, vertical motion downwards, horizontal motion).

Lastly, remember to always draw a free body diagram when you are looking at forces acting on an object. It will clear things up in almost every case.

5. Jan 13, 2009