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When a rifle is fired, the bullet accelerates from 0 to 1000 m/s (about 2240 mph) in 0.001 sec. What is the average acceleration of the bullet in meters per second squared? If this rate of acceleration could somehow be maintained, how long would the bullet take to reach the speed of light (about 300,000,000 m/s)?

 Feb 1, 2019
edited by Guest  Feb 1, 2019
 #1
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What a terrible question.

 

\(\bar{a} = \dfrac{|v| - |v_0|}{\Delta t} = \dfrac{1000-0~m/s}{0.001s} = 10^6 ~m/s^2\)

 

Ok, that's straight forward enough but the reason that the question is terrible is that 

it suggests that you can actually accelerate this bullet up to the speed of light.

 

I realize it's not a course on relativity but there's no reason to suggest that the impossible can be done.

 

The real answer to this question is that it will take forever the bullet to reach the speed of light because 

it cannot be reached by any sort of matter.

 

I suppose the answer they are looking for is

 

\(t = \dfrac{300 \times 10^6~m/s}{10^~m/s^2} = 300~s = 5~min\)

.
 Feb 1, 2019

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