2 bullets fired at the same time - find kinetic energies

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Homework Help Overview

The discussion revolves around calculating the kinetic energies of two bullets with given masses and velocities. The problem is situated within the context of classical mechanics, specifically focusing on kinetic energy calculations.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of the kinetic energy formula and the importance of unit conversion from grams to kilograms. There is an exploration of the calculations performed and the results obtained, with some participants expressing confusion over why their answers were marked incorrect.

Discussion Status

Some participants have identified issues with unit conversion and significant digits, leading to a realization of errors in their calculations. There is ongoing clarification regarding the proper handling of units and the implications for the final answers.

Contextual Notes

Participants are working under the constraints of a homework assignment that requires specific unit conversions and attention to significant figures. There is an acknowledgment of potential errors stemming from these constraints.

nn3568
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Homework Statement


Two bullets have masses of 4.7 g and 11 g, respectively. Each is fired with a speed of 39.0 m/s.
a) What is the kinetic energy of the first bullet? Answer in units of J.
b) What is the kinetic energy of the second bullet? Answer in units of J.
c) What is the ratio K2/K1 of their kinetic energies?

Homework Equations


KE = 1/2 mv2

The Attempt at a Solution


KE = 1/2 * 4.7g * (39.02 m/s)
and so on...

However, I do not know why the site is telling me my answers are wrong!
 
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Hi nn3568,

nn3568 said:

Homework Statement


Two bullets have masses of 4.7 g and 11 g, respectively. Each is fired with a speed of 39.0 m/s.
a) What is the kinetic energy of the first bullet? Answer in units of J.
b) What is the kinetic energy of the second bullet? Answer in units of J.
c) What is the ratio K2/K1 of their kinetic energies?

Homework Equations


KE = 1/2 mv2

The Attempt at a Solution


KE = 1/2 * 4.7g * (39.02 m/s)
and so on...

However, I do not know why the site is telling me my answers are wrong!

Did you convert the mass units to kg before entering the answer (if you leave it in grams the answer will not be in joules)? If so, what did you get?
 
Yes, I did convert it into kg when I did the problem again but the site still said I was wrong :(

my answers thus far:
3574.35 (w/o changing to kg)
1.833 (no idea)
35.7435 (change to kg)
0.01 (from a bad source :( )
 
OH i get what i did wrong. i messed up in converting!
 
Mind your significant digits.

Too many may not be good.
 

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