f.4PHYSICS 20 pts

Consider the first part,
initial velocity, u = 400 m/s
Final velocity, v= 200 m/s
Distance traveled, s = 7.5 cm = 7.5/100 m = 0.075 m
Equation of dynamics for uniform acceleration motion in a straight line.
v^2 = u^2 + 2as
200^2 = 400^2 + 2a(0.075)
a = - -800000 m/s^2 (negative sign indicates this deceleration.)

Consider the second part,
initial velocity, u = 200 m/s
Final velocity, v= 0 m/s (velocity = 0 when it stops)
Deceleration = - -800000 m/s^2
v^2 = u^2 + 2as
0^2 = 200^2 + 2(-800000)s
s = 40000/16000000.025 m = 2.5 cm

The bullet will penetrate 2.5 cm before it is stopped.



2010-12-25 08:50:40 補充：
Typo error in second part : missing the equal sign

s = 40000/1600000
= 0.025 m = 2.5 cm

2010-12-25 08:53:21 補充：
Better re-write part 2:

initial velocity, u = 200 m/s
Final velocity, v= 0 m/s (velocity = 0 when it stops)
Deceleration = - -800000 m/s^2
v^2 = u^2 + 2as
0^2 = 200^2 + 2(-800000)s
s = 40000/1600000 = 0.025 m = 2.5 cm

2010-12-25 08:56:01 補充：
Deceleration = - 800000 m/s^2 (one negative sign)