Inelastic collision kinetic energy lost?

AI Thread Summary
In an inelastic collision involving a bullet and a block of wood, the bullet's initial speed is 896 m/s, and after passing through, it slows to 435 m/s. The final velocity of the wood was calculated to be approximately 11.2 m/s. The kinetic energy lost during the collision is determined using the formula for kinetic energy, which requires squaring the velocities. A common mistake noted in the discussion is the incorrect handling of signs when calculating energy loss, emphasizing the importance of using the correct formula for kinetic energy loss. Proper application of conservation of momentum and careful calculation will yield accurate results for both final velocity and energy lost.
girl52
Messages
7
Reaction score
0
inelastic collision...kinetic energy lost?

Homework Statement


a bullet with a mass of 6 g is fired through a 1.25kg block of wood on a frictionless surface. initial speed of the bullet is 896 m/s and speed of bullet after it passes through it is 435 m/s. what's the final velocity? how much KE is lost?

Homework Equations


ke lost=ke initial-ke final
ke lost=1/2mvf-1/2mvi

i got 11.2 m/s for the final velocity of the wood

The Attempt at a Solution


KEi=1/2(.006)(896^2) + 0
KEf=1/2(.006)(435^2) + 1/2(1.25)(11.225^2)

i got 2408.228 - 488.925

thats not negative..where did i go wrong??
 
Last edited:
Physics news on Phys.org


Don't forget to square the velocity when calculating KE. But first try using conservation of momentum, and show your work, please.
 


edited
 


girl52 said:

Homework Statement


a bullet with a mass of 6 g is fired through a 1.25kg block of wood on a frictionless surface. initial speed of the bullet is 896 m/s and speed of bullet after it passes through it is 435 m/s. what's the final velocity? how much KE is lost?


Homework Equations


ke lost=ke initial-ke final
ke lost=1/2mvf-1/2mvi

i got 11.2 m/s for the final velocity of the wood
how did you arrive at this number?

The Attempt at a Solution


KEi=1/2(.006)(896^2) + 0
KEf=1/2(.006)(435^2) + 1/2(1.25)(11.225^2)

i got 2408.228 - 488.925

thats not negative..where did i go wrong??
The change in energy (final minus initial) is negative...if you use (initial minus final), you get your signs reversed. Don't do it that way, the minus signs are bad enough without compounding them.
 
Thread 'Voltmeter readings for this circuit with switches'
TL;DR Summary: I would like to know the voltmeter readings on the two resistors separately in the picture in the following cases , When one of the keys is closed When both of them are opened (Knowing that the battery has negligible internal resistance) My thoughts for the first case , one of them must be 12 volt while the other is 0 The second case we'll I think both voltmeter readings should be 12 volt since they are both parallel to the battery and they involve the key within what the...
Thread 'Correct statement about a reservoir with an outlet pipe'
The answer to this question is statements (ii) and (iv) are correct. (i) This is FALSE because the speed of water in the tap is greater than speed at the water surface (ii) I don't even understand this statement. What does the "seal" part have to do with water flowing out? Won't the water still flow out through the tap until the tank is empty whether the reservoir is sealed or not? (iii) In my opinion, this statement would be correct. Increasing the gravitational potential energy of the...
Back
Top