# Physics 161, Forces

1. Sep 21, 2011

### Kawasaki268F

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

1. A 340 kg rocket sled can be accelerated at a constant rate from rest to 1900 km/h in 2.6 s. What is the magnitude of the required net force?

2. Relevant equations

3. The attempt at a solution
1. So I tried calculating the acceleration and multiplying it by the mass. For the acceleration I tried dividing 1900km/h by 2.6s and multiplying it by the mass however that did not work.

2. Sep 21, 2011

### PeterO

This may sound silly, but you did convert the 1900 km/h to m/s didn't you?

3. Sep 21, 2011

### C268

Yes sorry I did do that, forgot to mention that above

4. Sep 22, 2011

### PeterO

Ok approximating

1900km/h is a little over 500 m/s

A little over 500 in 2.6 must be about 500 in 2.5 seconds so acceleration is around 200 ms-2

F = ma says 200 * 340 so approx 68 000 N

5. Sep 22, 2011

### Kawasaki268F

Sweet thanks! I just forgot about the squared part on 200m/s

6. Sep 22, 2011

### PeterO

Are you saying the only error you had was in the units of an answer??? because none of the numbers in this problem are squared?????