Unit Conversions and Mistakes: Understanding the Basics

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The discussion centers on confusion regarding unit conversions in physics, specifically when calculating average force. The user presents a problem involving a football's mass, speed, and contact time, but struggles with the final units of their calculation. They mistakenly believe their result is incorrect despite it being in Newtons, as the units kg·m/s² are indeed equivalent to Newtons. The conversation highlights the importance of understanding unit consistency and the correct application of formulas in physics. Taking a break from the problem-solving process is suggested to alleviate frustration.
gcombina
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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)
 
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Those units of yours are the same as Newtons.

Chet
 
of course :redface:

i think I need a break

Thanks!
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
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