# Homework Help: Finding acceleration from distance and time

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1. Feb 22, 2016

### ajd2000

1. The problem statement, all variables and given/known data
A bullet with a mass of m=15.5 g is shot out of a rifle that has a length of L=1.02 m. The bullet spends t=0.16 s in the barrel.

Write an expression, in terms of given quantities, for the magnitude of the bullet's acceleration, a, as it travels through the rifle's barrel. You may assume the acceleration is constant throughout the motion.

So I'm supposed to write an acceleration equation using L and t but everything I try it says is wrong and the only hints are to use the given information and that theres a 2 somewhere in the numerator.

2. Relevant equations
I'm trying to find the equation. But I assume that V= d/t is used somehow and then a=v(final)+v(initial) / t is also used

3. The attempt at a solution
I tried just putting d/t (or L/t) where v goes in the acceleration equation but it says there's a 2 somewhere in the numerator that is also somehow related to L. So I tried squaring L and also L/t but neither of those was right and I also tried putting (2(L/t))/t which was also wrong. I only have one guess left before I just get a 0 on this part of the problem and the rest of the problem requires this formula (I tried to figure out the rest without doing this part but couldn't).

2. Feb 22, 2016

### Staff: Mentor

3. Feb 22, 2016

### Cozma Alex

In an uniform accelerated motion the space travelled by a particle at any time is given by x(t)=1/2at^2

With the initial condition: V(initial)= 0 and x(initial)=0

Last edited: Feb 22, 2016