A 7.80-g bullet moving at 680 m/s penetrates a tree trunk to a depth of 5.20 cm.
ID: 1480439 • Letter: A
Question
A 7.80-g bullet moving at 680 m/s penetrates a tree trunk to a depth of 5.20 cm. (a) Use work and energy considerations to find the average frictional force that stops the bullet.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 A 7.80-g bullet moving at 680 m/s penetrates a tree trunk to a depth of 5.20 cm. (a) Use work and energy considerations to find the average frictional force that stops the bullet.
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 (a) Use work and energy considerations to find the average frictional force that stops the bullet.
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
Explanation / Answer
a)
here by using the formula
KE = 0.5 * m * v^2
and
W = F * d
This work must equal the energy of the bullet, as the hero must work to overcome the kinetic energy:
F * d = 0.5 * m * v^2
F = (0.5 * 7.8 * 10^-3 * 680) / 0.052
F = 34680 N
b)
F = m * a
and
d = 0.5 * a * t^2
then
d = 0.5 * (F / m) * t^2
t = sqrt( (2 * 0.052 * 0.0078) / 34680)
t = 0.0001529 sec
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