Physics problem?

Question

The Beretta Model 92S (the standard-issue U.S. army pistol) has a barel 127mm long. The bullets leave this barrel with a muzzle velocity of 335m/s.

a) What is the acceleration of the bullet while it is in the barrel, assuming it to be constant? Express your answer in m/s^2 and in g's.
b) For how long is the bullet in the barrel?

Answer:
a) 4.42 x 10^5m/s^2 = 4.51 x 10^4g
b) 0.758 ms

I need to know how to get the answer. Please help.

Answer 1

Some uninformed soul gave Bekki a thumbs down. What she answered is 100% correct, but you have to do the math.

The physics is that the work performed (W) on the bullet while in the barrel results in the bullet's kinetic energy (KE) as it emerges from the barrel...that's conservation of energy at work (pun intended). In fact, the potential energy of the gunpowder is first converted to force (F) (from PV = nRT), which is then put to work on the bullet to be converted to kinetic energy as the bullet comes out of the muzzle.

Thus, in math talk, W = Fd = mad = 1/2 mv^2 = KE. Indeed, the bullet mass cancels out to leave us with ad = 1/2 v^2; so that the bullet acceleration is a = (1/2d) v^2; where d = 127 mm = 127 X 10^-3 m and v = 335 m/sec. n = number of g's = a/g; where g = 9.81 m/sec^2 at Earth's surface.

The old SUVAT equation v = u + at can be used to find t, the time in the barrel. v is given and you just calculated a. u, the starting velocity of the bullet, = 0. Thus we have t = v/a and you can do the math.

Answer 2

Conservation of energy
Work done = Force * distance
= m a d
=
Kinetic energy = 1/2mv^2

a = v^2 / 2d

acceleration in g's = a/g = v^2 / 2dg

b) To get the time, use distance = 1/2 at^2

so t = sqrt (2d/a) = 2d / v

Answer 3

Using the equations of motion;

v^2 = u^2 + 2 as and since u = 0, v^2 = 2as.

a = v^2 /2s = 335^2 / [2 * 0.127] = 4.42 e+5 m/s^2

9.8 m/s^2 = one g.

4.42 e+5 m/s^2 = 4.42 e+5 / 9.8 = 4.51 x 10^4 g
-----------------------------------------------------------------

To find time use
s = average velocity x time
Time = 2 *[0.127 / 335] = 7.58e-4 s = 0.758 ms

Answer 4

the galaxies rotate at speeds inconsistent with their obvious mass is as a results of the fact we do see all of it. i'm bearing on it as being the theoretical dark count number. There are very sturdy proofs that shows that dark count number exist. One the is the inconsistent speed of and obvious mass. dark count number makes up approximately 75% to 80% of the problem in the Universe...