Write-Up Assignment for Lab 4:

A Ballistic Projectile

Physics 203: Prof. Daniel Yaverbaum & Prof. Anil Asokan

John Jay College of Criminal Justice, the CUNY

As usual, submit a 4-part Lab Report.

Part I: Cover Sheet.

Part II: Answers to Triple-Starred and Special Instructions.

--During this part, answer all the questions below.

A) Make certain that your write-up includes responses to all the D and Q prompts from the original lab assignment: reprinted at the bottom of this page. They will serve as "triple-starred" questions.

B) The bullet emerging from a ballistic pendulum is fired, not merely dropped. Why, then, does this experiment make use of time required for a stationary object to fall from a given height? Put a different way, How can this 'free-fall' time correctly apply to a horizontal projectile?

C) In at least one complete paragraph, explain the relationship between the laws of physics and the practice of forensic science--as seen through this experiment.

Part III: Full Methods & Findings Section.

For this section, your final conclusion must look something like the following:
 

Weapon Location  = _____________________ cm +/- ____________________ cm from Target Location.

There may be some redundancy and expansion from responses to Part II. That's fine.Two distinct purposes are being served.

If/when you feel that you are about to write something for Part III that you have already fully and sufficiently covered in Part II, then you may make an explicit reference to an earlier description (such as "see Section ____, Page ______) or something to that effect.

Make fully certain that you thoroughly explain whether your conclusion did or did not lead to a successful firing.  Perform a careful and fully numerical uncertainty analysis (in the manner we have been doing all semester) and explain why the extent to which any imperfections in the firing test could be accounted for by measurement uncertainty.  If measurement uncertainty did not fully account for imperfections, then explain what else might have contributed.

Part IV: Appendices

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To refresh your recollection, here are the

ORIGINAL LAB EXCERPTS:

        Ultimate Objectives:

    1. To apply the principles underlying projectile motion so as to make a verifiable retrodiction.

    2. To probe the connection between Galileo's Principle of Relativity (esp. "Form 4") and the principles underlying projectile motion.

    3. To use the laws of physics in a vivid forensic investigation.

   4. To not get hurt.

        Immediate Objectives:

    1. To determine where a "weapon" (ballistic pendulum) must have been located if a "bullet" (brass sphere) hit a particular target.

        --> Specifically, to use analysis and computations (rather than trial and error) to determine where you must place your ballistic pendulum so that it successfully fires a brass sphere into a cup.

    2. To not get hurt.

   Q1: In 1 - 3 complete sentences of English, explain what you measured for a displacement and why this measurement is relevant for a calculation of the sphere's velocity through the photogate.

D1: Let x Ξ Horizontal Displacement.  In centimeters, enter your displacement: x = ________________ cm.

   D2:

IV. The Vertical Component.

    A. Using your meter stick, measure the height from which your sphere will be fired from the ballistic pendulum.

D3: Let y =  Vertical Displacement.   In centimeters, enter your displacement: y = ____________________ cm.  

  B. Determine how much time [sec] an object dropped from rest would take to free-fall the vertical displacement you obtained above.

D4: Let t =  Free-Fall Time.   In seconds, enter your time: t = ____________________ sec.  

V. Synthesis.

    A. If you think about it hard enough, you will see that you now have all the information you need in order to make a retrodiction.

    B. Place your target (cup) at some appropriate and reasonable location on the floor.  Using masking tape, secure the target.

    C. This target represents something or someone that, if you do everything correctly, will have gotten shot.

    D. Assume that the weapon had been at the height you measured.  Do whatever calculations you need to determine:

        At what (horizontal) range from the target was the weapon?