A rifle with a barrel length of 60 cm fires a 10 g bullet with a horizontal speed of 400 m/s. The bullet strikes a block of wood
and penetrates to a depth of 12 cm. . a. what resistive force (assumed to be constant) does the wood exert on the bullet? . b. How long does it take the bullet to come to rest? . c. Draw a velocity verses time graph for the bullet in the wood.
2 answers:
consider the motion of bullet as it penetrates through the block
v₀ = initial velocity of the bullet = 400 m/s
v = final velocity of the bullet = 0 m/s
d = distance traveled = 12 cm = 0.12 m
a = acceleration = ?
Using the equation
v² = v₀² + 2 a d
0² = 400² + 2a (0.12)
a = - 6.67 x 10⁵ m/s²
m = mass of the bullet = 10 g = 0.010 kg
The resistive force is given as
f = ma
inserting the values
f = (0.010) (- 6.67 x 10⁵ )
f = - 6670 N
b)
t = time taken by the bullet
using the equation
v = v₀ + a t
0 = 400 + (- 6.67 x 10⁵ ) t
t = 6 x 10⁻⁴ sec
c)
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