# Catching up

1. Oct 25, 2005

### jdenn

Hi, ive got a big probllem:

When you are 20m away from your bus it begins accelerating a 3m/s/s (from rest). What constant velocity should you run at to catch the bus.

HELP!!!!!!!!!!!!!!!
jason

2. Oct 25, 2005

### suspenc3

theres i big chance no one will help you unless you show an attempt

3. Oct 25, 2005

### Tom Mattson

Staff Emeritus
Yep, you have to show that you've made an attempt.

4. Oct 25, 2005

### jdenn

thats the think I have no idea where to begin

The fruit of my labors is:
me:
Vi=?
Vf=?
t=?
a=0
d=to bus

bus:
Vi=0
Vf=?
t=?
a=3m/s^2
d=to bus
This enough? because otherwise i am sol

Last edited: Oct 25, 2005
5. Oct 25, 2005

### *melinda*

Try drawing two pictures; the first showing the initial conditions, and the second showing the final conditions when you've caught the bus.

Once you've drawn the pictures, make sure you listed all your knowns.

List your kinematics formulas so you can see what you have to work with.

And don't forget to note your initial and final position.

Try choosing your initial position as zero, which would make the initial position of the bus 20 m.

6. Oct 25, 2005

### jdenn

Re:

i have drawn a picture, listed my formulas( no idea which 1 to use though)

7. Oct 25, 2005

### Tom Mattson

Staff Emeritus
You have yet to make use of that 20m in the problem statement. Let the motion be along the x-axis.

Can you fill in the following information?

Runner: xi=?
Bus: xi=?

8. Oct 25, 2005

### jdenn

ive been working more but all i have still is:thats the think I have no idea where to begin

me:
Vi=?
Vf=Vi (constant)
t=?
a=0
d=to bus-20

bus:
Vi=0
Vf=?
t=?
a=3m/s^2
d=to me+20

9. Oct 25, 2005

### Tom Mattson

Staff Emeritus
In order to answer my question, you need to choose an origin for the coordinate system. Let's just put the runner's initial position at the origin, and let the bus sit to the right of the runner.

Now can you fill in those values?

10. Oct 25, 2005

### jdenn

me:
Vi=?
Vf=Vi (constant)
t=?
a=0
d=distance run

bus:
Vi=0
Vf=?
t=?
a=3m/s^2
d=to run-20

11. Oct 25, 2005

### Tom Mattson

Staff Emeritus
What I am asking you to do is assign an x-coordinate to both the runner and the bus initially. Do you know what a coordinate on a graph is?

12. Oct 25, 2005

### jdenn

x would be distance and y would be time right?

13. Oct 26, 2005

### Tom Mattson

Staff Emeritus
In the usual notation, x is distance and t is time. So if you have motion in 1 dimension, and we say that the motion is along the x-axis, and we say that the runner starts at the origin and that the bus starts out 20 meters to the right of the runner, then can you please tell me what the initial x-coordinate of both the runner and the bus are?

We're happy to help with homework, but you have to work with us.