# Stuck on this simple physics problem.

1. Sep 21, 2010

### pokeefer

1. The problem statement, all variables and given/known data

Two buses are moving at constant speeds, in the same direction, the first at 42 km/h and the second at 54 km/h. They are 18 km apart. How long will it take the second bus to catch up to the first? (4 marks)

2. Relevant equations

average velocity = d/t

3. The attempt at a solution

Ok well first I tried to make a table of the graph but then I remembered that they were 18 km apart so then I had to rethink and I'm still really stuck on this.

2. Sep 21, 2010

### rl.bhat

When they catch up, the first bus moves through x km and second bus moves through x + 18 km, and they must have taken the same time to cover that distance.

Can you proceed now?

3. Sep 21, 2010

### pokeefer

What would be a formula that could solve for this?

Or do I have to use a table?

4. Sep 21, 2010

### rl.bhat

Velocity = x/t. So t = x/v.

Since t is the same

x/v1 = (x+18)/v2

v1 and v2 are given. Solve for x.