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Introductory Physics Homework Help
Find momentum transfer and force on the head with and without a helmet
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[QUOTE="erobz, post: 6852218, member: 700856"] If the head were moving to the right ##\rightarrow^+## then the force from the collision would be to the left ##\leftarrow^-##. So that would look like: $$ \vec{F_{avg}} \Delta t = 0 - m \vec{v_o} \implies \vec{F_{avg}} = -\frac{m \vec{v_o} }{\Delta t}$$ If ##\vec{v_o} = v_o \boldsymbol{u}## is positive (1D) the average Force is to the left (negative), you would find: $$\vec{F_{avg}} = -\frac{m v_o \boldsymbol{u} }{\Delta t}$$ Where ##\boldsymbol{u}## is just a unit vector for the positive direction. However, you could just as easily choose the right as positive and have the head moving to the left. In which case you would find after substituting ##\vec{v_o} = -v_o \boldsymbol{u}##: $$ \vec{F_{avg}} \Delta t = 0 - m \vec{v_o} \implies \vec{F_{avg}} = \frac{m v_o }{\Delta t} \boldsymbol{u} $$ Basically, the directions are arbitrary here. The magnitudes of the forces aren't. That took me a few edits once I looked at what I was saying. I hope I didn't confuse you along the way. [/QUOTE]
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Find momentum transfer and force on the head with and without a helmet
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