Homework Help: Kinematics physics question

1. Feb 18, 2010

seanspan

1. The problem statement, all variables and given/known data
There are two towns that are 20km apart. A biker leaves town#1 travelling at 20km/h and at the same time another biker leaves town#2 travelling at 15km/h. Where and when will they meet?
Given
d=20km between 2 towns
V biker 1=20km/h
V biker 2=15km/h

2. Relevant equations
d=v1t+1/2at^

3. The attempt at a solution
I know that you have to somehow make two equations and make them equal to each other and then solve for d and sub it into one of the equations to solve for t but im having trouble starting please help

Last edited: Feb 18, 2010
2. Feb 19, 2010

Keldon7

Think of what will be equal for both bikers when they meet. Is the distance they've traveled the same? The time perhaps?

3. Feb 19, 2010

seanspan

well the time will be equal i know that im just having trouble with how to set it up. I assume you have to make 2 equations and then make them equal to each other im just not sure what the equations should be.

4. Feb 19, 2010

hotvette

Correct, you'll have two equations that you'll need to equate. But, the applicable equation really should be the general form d = d0 + v0t + 1/2at2 where d0 represents the initial distance (i.e. postion) at t=0 with respect to a chosen coordinate system/origin. For example, if you choose the origin to be the initial starting point of the 1st biker, then d0 = 0 for the 1st biker. Using the same origin, think about what d0 would be for the 2nd biker and what happens over time. In the end, you want to find the time at which both bikers are in the same position (with respect to the same orgin), and from that you can find the location. When you write the equations, be careful to use the correct sign for each term based on the origin and direction of postive distance that you choose.

A different (and perhaps easier) approach would be to write a single equation that represents the distance between the two bikers. The time you are looking for is the time at which the distance between them is zero.

Last edited: Feb 19, 2010