MY NOTES

SERCP$115\mathrm{.}2.$P$\mathrm{.}015.$

A $7\mathrm{.}80-g$ bullet moving at $640\frac{m}{s}$ penetrates a tree trunk to a depth of $6\mathrm{.}20$ cm $.$

$($a$)$ Use work and energy considerations to find the average frictional force that stops the bullet. $($Enter the magnitude.$)$

$$ N

$($b$)$ Assuming the frictional force is constant, determine how much time elapses between the moment the bullet enters the tree and the moment it stops moving.

$$ s