Calculating the Distance of a Block from a Table After a Bullet Collision

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Homework Help Overview

The problem involves a bullet colliding with a block of wood at the edge of a table, with the goal of determining how far the block lands from the table after falling. The subject area encompasses concepts of momentum, kinematics, and projectile motion.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the calculation of the final velocity after the bullet embeds in the block and the time it takes for the block to fall from the table. Questions arise regarding the accuracy of the time calculation and the method used to determine it.

Discussion Status

There is an ongoing examination of the calculations presented, particularly concerning the time of fall and the application of formulas. Some participants suggest that the original poster may be miscalculating the time based on incorrect assumptions or unit handling.

Contextual Notes

Participants note a potential typo in the gravitational constant used for calculations, which may have contributed to confusion. The discussion reflects a focus on ensuring correct unit usage and understanding the relationships between distance, time, and acceleration.

mikefitz
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A 0.01-kg bullet traveling horizontally at 400.1 m/s strikes a 4.2-kg block of wood sitting at the edge of a table. The bullet is lodged into the wood. If the table height is 1.3 m, how far from the table does the block hit the floor?

I have calculated the final velocity of the bullet and block to be:

.01(400.1)=.01(Vf)+4.2(Vf)

Vf= .9504 m/s

So, now I have the velocity of the bullet embedded into the block. The time in the air is 1.3/9.82 = .1325 seconds.

.1325s * .9504 m/s = .1259 meters

Why is this wrong? Thanks
 
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mikefitz said:
So, now I have the velocity of the bullet embedded into the block. The time in the air is 1.3/9.82 = .1325 seconds.
How did you determine this? How long does it take for something to fall 1.3 meters?
 
mikefitz said:
Why is this wrong? Thanks
Your calculated time in air is wrong.
 
OlderDan said:
Your calculated time in air is wrong.

Sorry, I meant to type 1.3/9.81 = .1325 -- the 9.82 was a typo.
 
mikefitz said:
Sorry, I meant to type 1.3/9.81 = .1325 -- the 9.82 was a typo.
That is not the problem. You are not calculating time. It would help you to keep your units in your calculations. Distance divided by acceleration is not time.
 
Stupid me, I used this formula and found the correct answer: http://www.glenbrook.k12.il.us/gbssci/Phys/Class/1DKin/U1L6b4.gif

thanks!
 
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