Turn on thread page Beta
    • Political Ambassador
    • Thread Starter
    Offline

    12
    ReputationRep:
    Political Ambassador
    Name:  Mechanics 2.jpg
Views: 19
Size:  423.1 KB
    I did the a) part but I could not do the b) part. This relates the law of conservation of momentum. Anyone, suggestions please!
    Offline

    15
    ReputationRep:
    (Original post by Rashina)
    Name:  Mechanics 2.jpg
Views: 19
Size:  423.1 KB
    I did the a) part but I could not do the b) part. This relates the law of conservation of momentum. Anyone, suggestions please!
    You've found the initial velocity of the recoil. It goes to rest after moving 2cm. What is the acceleration of the rifle as it loses velocity?

    Hence, what is the force acting on it? (F=ma)
    • Political Ambassador
    • Thread Starter
    Offline

    12
    ReputationRep:
    Political Ambassador
    (Original post by K-Man_PhysCheM)
    You've found the initial velocity of the recoil. It goes to rest after moving 2cm. What is the acceleration of the rifle as it loses velocity?

    Hence, what is the force acting on it? (F=ma)
    Check whether it is correct:
    My working:

    v=0 m/s
    u=2.08 m/s
    s=0.02 m
    a=?

    v2= u2+2as
    0=4.3264 + 2as
    2as= -4.3264
    a= -108.16

    F=ma
    F= 6 x 108.16
    F=648.96
    F=649N (to 3s.f)

    I checked the answer in the book. It is different. It is 0.651kN or 651N. Why didn't my answer match?
    Offline

    15
    ReputationRep:
    (Original post by Rashina)
    Check whether it is correct:
    My working:

    v=0 m/s
    u=2.08 m/s
    s=0.02 m
    a=?

    v2= u2+2as
    0=4.3264 + 2as
    2as= -4.3264
    a= -108.16

    F=ma
    F= 6 x 108.16
    F=648.96
    F=649N (to 3s.f)

    I checked the answer in the book. It is different. It is 0.651kN or 651N. Why didn't my answer match?
    That will be down to a rounding error most likely. What was the exact value for velocity that you got from part (a) (not the rounded version of 2.08m/s)? You should leave answers to the stated accuracy, but never round off early in calculations, even if you rounded to give an answer to the first part of a question.

    eg
    If initial velocity was actually 2.083, but you rounded to 2.08:
    F = 6 \times \dfrac{2.083^2}{2\times0.02} = 650.833...N = 651 N
    • Political Ambassador
    • Thread Starter
    Offline

    12
    ReputationRep:
    Political Ambassador
    (Original post by K-Man_PhysCheM)
    That will be down to a rounding error most likely. What was the exact value for velocity that you got from part (a) (not the rounded version of 2.08m/s)? You should leave answers to the stated accuracy, but never round off early in calculations, even if you rounded to give an answer to the first part of a question.

    eg
    If initial velocity was actually 2.083, but you rounded to 2.08:
    F = 6 \times \dfrac{2.083^2}{2\times0.02} = 650.833...N = 651 N
    The answer for a) part was actually 25/12 which is 2.083333... and I rounded it. Thanks for your help. Could you help me in one more problem please? Its in the link below:
    http://www.thestudentroom.co.uk/show....php?t=4400030
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: November 6, 2016
The home of Results and Clearing

2,888

people online now

1,567,000

students helped last year

University open days

  1. SAE Institute
    Animation, Audio, Film, Games, Music, Business, Web Further education
    Thu, 16 Aug '18
  2. Bournemouth University
    Clearing Open Day Undergraduate
    Fri, 17 Aug '18
  3. University of Bolton
    Undergraduate Open Day Undergraduate
    Fri, 17 Aug '18
Poll
Do you want your parents to be with you when you collect your A-level results?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

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.