Trouble finding the magnitude of a net force required.

[mcaustin]

Here is the problem I have:
1. A 800 kg rocket sled can be accelerated at a constant rate from rest to 1500 km/h in 2.1 s. What is the magnitude of the required net force?

First I converted the a from 1500 km/h to 416.7 m/s
I then used F=ma but I got the result as 333360 N but this answer is incorrect. I'm not quite sure where to go from here and I don't know what the significance of time is. I used it to calculate velocity using v=at and got 875.07 m/s but I don't know how is should use it, if at all.

Thanks for any help anyone can give!

 

[mcaustin]

I figured out my mistake!
I thought that 416.7 was acceleration but it is actually velocity.