Firearm injuries: kinetic energy of the bullet: practice question

A Forensic Medicine question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Forensic Medicine · Firearm injuries: kinetic energy of the bullet

Sample item

Two bullets of the same mass (10 g) are fired, one at 300 m/s and one at 600 m/s. Compared with the first, the kinetic energy of the second is:

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Four times as great (1800 J versus 450 J)

Kinetic energy is half mass times velocity squared. For 0.01 kg at 300 m/s it is 0.5 x 0.01 x 90,000 = 450 J; at 600 m/s it is 0.5 x 0.01 x 360,000 = 1800 J. Doubling the velocity quadruples the energy, which explains the larger temporary cavity and tissue damage of high-velocity missiles.

Option by option

  • A. Eight times as great (3600 J versus 450 J)

    Eight times would need energy to rise with the cube of velocity.

  • B. Equal, because the mass is the same

    Mass is equal but velocity is not, and energy depends on velocity squared.

  • C. Twice as great (900 J versus 450 J)

    Twice would be the result if energy were proportional to velocity.

  • D. Four times as great (1800 J versus 450 J) (correct)

    Correct. Energy rises with the square of velocity, so doubling gives four times.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is D, Four times as great (1800 J versus 450 J). Kinetic energy is half mass times velocity squared.

Why is "Eight times as great (3600 J versus 450 J)" not the answer?

Eight times would need energy to rise with the cube of velocity.

Why is "Equal, because the mass is the same" not the answer?

Mass is equal but velocity is not, and energy depends on velocity squared.

Why is "Twice as great (900 J versus 450 J)" not the answer?

Twice would be the result if energy were proportional to velocity.

What concept does this question test?

It tests Firearm injuries: kinetic energy of the bullet in Forensic Medicine. For 0.01 kg at 300 m/s it is 0.5 x 0.01 x 90,000 = 450 J; at 600 m/s it is 0.5 x 0.01 x 360,000 = 1800 J. Doubling the velocity quadruples the energy, which explains the larger temporary cavity and tissue damage of high-velocity missiles.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Firearm injuries: kinetic energy of the bullet?

Learn postmortem changes with their timelines, and toxicology as poison, sign, test and antidote. Then use the flashcards and the other Forensic Medicine questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.