Unit Conversions and Mistakes: Understanding the Basics

[gcombina]

Hello, I am having lots of problems with units. I don't know why but I am getting sick of it. I don't know what am I doing wrong.

Let me give you an example.

I have this problem:
A football player kicks a 0.41-kg football initially at rest; and the ball flies through the air. If the kicker's foot was in contact with the ball for 0.51 s and the ball's initial speed after the collision is 21 m/s, what was the magnitude of the average force on the football?

My attempt:

F = mv/t
F = (0.41 kg) (21m/s) / 0.051s
F = (8.61 Kg. m. / s) / 0.051 s
F = (8.61 kg.m) / 0.051 s^2
F = 169 kg.m/s^2

why is my unit so wrong? (kg.m/s^2) (my answer should be in NEWTONS)

 

[Chestermiller]

Those units of yours are the same as Newtons.

Chet

 

[gcombina]

of course

i think I need a break

Thanks!