Turn on thread page Beta

A level physics edexcel specimen paper 1 question watch

    • Thread Starter
    Offline

    0
    ReputationRep:
    A bullet is fired into a block of wood. why would both the kinetic energy and momentum not be conserved?
    Offline

    1
    ReputationRep:
    (Original post by franceskkl)
    A bullet is fired into a block of wood. why would both the kinetic energy and momentum not be conserved?
    It must be because it’s a none elastic collision
    Offline

    0
    ReputationRep:
    (Original post by franceskkl)
    A bullet is fired into a block of wood. why would both the kinetic energy and momentum not be conserved?
    Is there any chance that you could send me a copy of this paper please🙂
    Offline

    3
    ReputationRep:
    external forces act on the system and the wood is deformed meaning energy must be transfered.
    Offline

    7
    ReputationRep:
    (Original post by franceskkl)
    A bullet is fired into a block of wood. why would both the kinetic energy and momentum not be conserved?
    Like others have said, this is an inelastic collision so KE isn't conserved. Some of the energy is transferred to thermal through the friction of the wood.

    However momentum is always conserved when there are no external forces applying on the system hence there is no acceleration.

    This question is asking why momentum isn't conserved and that is due to an external force, such as a drag (resistance to the motion of the bullet) and possibly if the wooden block was on a rough surface, a frictional force would be causing a deceleration to it.

    Quite simply, because air resistance and possibly resistance to the motion of the block is causing an acceleration hence the velocity will not be constant hence momentum isn't conserved. KE is also lost to sound, heat (Due to friction) as this is not an elastic collision.
    Offline

    21
    ReputationRep:
    (Original post by TheTechnoGuy)
    Like others have said, this is an inelastic collision so KE isn't conserved. Some of the energy is transferred to thermal through the friction of the wood.

    However momentum is always conserved when there are no external forces applying on the system hence there is no acceleration.

    This question is asking why momentum isn't conserved and that is due to an external force, such as a drag (resistance to the motion of the bullet) and possibly if the wooden block was on a rough surface, a frictional force would be causing a deceleration to it.

    Quite simply, because air resistance and possibly resistance to the motion of the block is causing an acceleration hence the velocity will not be constant hence momentum isn't conserved. KE is also lost to sound, heat (Due to friction) as this is not an elastic collision.
    Nah momentum is always conserved, mistake in the question, edexcel released an erratum notice
    Offline

    7
    ReputationRep:
    (Original post by glad-he-ate-her)
    Nah momentum is always conserved, mistake in the question, edexcel released an erratum notice
    Momentum is only conserved when external forces (such as drag) are not applying on the system. It's not always conserved.

    If it said in the question resistances to motion is negligible, then you're point would be valid, but this isn't case since he hasn't posted the full question.
    Offline

    21
    ReputationRep:
    (Original post by TheTechnoGuy)
    Momentum is only conserved when external forces (such as drag) are not applying on the system. It's not always conserved.

    If it said in the question resistances to motion is negligible, then you're point would be valid, but this isn't case since he hasn't posted the full question.
    Yeah i meant in a system with no external forces, ive seen this question and it said assume no external resistive forces, but of course you had no way of knowing that.
 
 
 

University open days

  1. University of Bradford
    University-wide Postgraduate
    Wed, 25 Jul '18
  2. University of Buckingham
    Psychology Taster Tutorial Undergraduate
    Wed, 25 Jul '18
  3. Bournemouth University
    Clearing Campus Visit Undergraduate
    Wed, 1 Aug '18
Poll
How are you feeling in the run-up to Results Day 2018?
Help with your A-levels

All the essentials

The adventure begins mug

Student life: what to expect

What it's really like going to uni

Rosette

Essay expert

Learn to write like a pro with our ultimate essay guide.

Uni match

Uni match

Our tool will help you find the perfect course for you

Study planner

Create a study plan

Get your head around what you need to do and when with the study planner tool.

Study planner

Resources by subject

Everything from mind maps to class notes.

Hands typing

Degrees without fees

Discover more about degree-level apprenticeships.

A student doing homework

Study tips from A* students

Students who got top grades in their A-levels share their secrets

Study help links and info

Can you help? Study help unanswered threadsRules and posting guidelines

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.