How to find velocity of a bullet given energy?

AI Thread Summary
To find the velocity of a bullet given its energy, the discussion revolves around using the work-energy principle. The bullet, with a mass of 15 grams, is subjected to a constant force of 7200 N over a distance of 0.85 meters, resulting in a calculated work of 6120 J. This work is then equated to the bullet's kinetic energy, leading to the equation 6120 J = 1/2(0.015)v^2. The resulting calculation yields a velocity of 903 m/s, but there is uncertainty about the correctness of this value. The conversation emphasizes verifying the accuracy of input values and understanding the relationship between work and kinetic energy.
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Homework Statement


A bullet with a mass of 15 grams is fired from a rifle with a barrel that is 85 cm long.
a. assuming that the force exerted by the expanding gas to be a constant 7200N, what speed would the bullet reach?


Homework Equations


Ek= 1/2mv^2
Work= Force x distance


The Attempt at a Solution



Originally I thought that 7200 N were equal to Energy Kinetic so I solved like that
7200N=.5(.015)v^2...
but that seems to be incorrect.

So I found the equation for work
So I tried doing
work= 7200N x .85 meters work = 6120 J
Then setting that equal to Ek so...
6120J= 1/2(.015)v^2
v= 903 m/s
But that also seems to be incorrect.
Am I missing a step? Or am I using the wrong equation?

Please Help me, thank you in advance.
 
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Work is energy, so in the case where the work accelerates a bullet, the work is the same as the change in kinetic energy. W=ΔE_k

Thus, your calculations should be correct... Are you sure all the values are correct? What is the answer supposed to be?
 

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