1. The speed of a bullet is measured to be 640 m/s as the bullet emerges from a

Question

1. The speed of a bullet is measured to be 640 m/s as the bullet emerges from a barrel of length 1.20m. Assuming the intial speed of the bullet is zero and a constant positive acceleration in the barrel, find the time that the bullet spends in the barrel after it is fired.

I HAVE ALREADY SOLVED THIS. Just posting for referrence.

2. Please explain why we assume the initial speed of the ublet is zero together with a constant postive acceleration in the barrel in problem 1 above.

3. Can we solve problem 1 if we assume a constant negative acceleration in the barrel (without assuming initial speed of the bullet to be zero)?

Explanation / Answer

1)

v^2 = u^2 + 2*a*s

640^2 = 0 + 2*a*1.2

a = 170666.66

Hence

v = u + at

640 = 170666.66*t

t = 0.0037 sec

2) The bullet was at rest so the u = 0

3) Nope

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