# Homework Help: Average Speed/Velocity

1. Sep 8, 2009

### Loppyfoot

1. The problem statement, all variables and given/known data
A car making a 200-km journey travels 50 km/h for the first 100 km. How fast must the car go in the second 100 km to average 60 km/h?

2. Relevant equations
There is the average velocity equation, and also the average speed equation.
(delta x)/(delta t) = average velocity
average speed = total distance/total time

3. The attempt at a solution
50 = 100/t
to get the time? Do I need to do that?
Then should I do the same for the next one?

2. Sep 8, 2009

### rl.bhat

t1 = 100/50 s
t2 = 100/v s
Total distance is given.
Average velocity is given. Total time t = t1 + t2.
Substitute these values in the relevant equation to find v.

3. Sep 8, 2009

### Loppyfoot

Ok, so ,
t1 = 2s
t2 = 100/v s

The total distance is 200km. The average velocity for the 2nd portion is 60km/h. I do not have t2, because I don't have v. I am confizzled.

4. Sep 8, 2009

### rl.bhat

Total time t = 200m/60 km/h.
t1 is known. Find t2. Then find v.