Hey there! Sign in to join this conversationNew here? Join for free

Mechanics 1 help Watch

Announcements
    • Political Ambassador
    • Thread Starter
    Offline

    20
    ReputationRep:
    just when i thought i never have to do physics again :cry:


    anyways, i've jsut started suvat equation/rectilinear motion

    a train travelling on straight rail, from A to B.
    acceleration = -0.6ms^-2
    u = 72km/h
    t = 25s
    find the final velocity in km/h.

    i know im using the equation v=u+at

    v=72+(-0.6*25?)
    do i use the time in seconds or convert it into hours? (and why? I'm curious)
    • Very Important Poster
    Online

    21
    ReputationRep:
    (Original post by ihatePE)
    just when i thought i never have to do physics again :cry:


    anyways, i've jsut started suvat equation/rectilinear motion

    a train travelling on straight rail, from A to B.
    acceleration = -0.6ms^-2
    u = 72km/h
    t = 25s
    find the final velocity in km/h.

    i know im using the equation v=u+at

    v=72+(-0.6*25?)
    do i use the time in seconds or convert it into hours? (and why? I'm curious)
    Use consistent units and you will get the answer in the same units.

    Eg if you were adding 5 hours to 40 minutes then you would not say t = 5 + 40. You would either convert 40 minutes to 2/3 hours to give t = 5 + 2/3, so you know that the answer is in hours, or alternatively t = 5*60 + 40, so you know that the answer is in minutes. As you have acceleration (already in m/s^2) you would need to be very careful as well. Best to stick to seconds for that reason (unless your answer requires km/h which I have just seen :lol:)
    Offline

    15
    ReputationRep:
    You need to use the same units throughout a calculation.

    If you are talking about km/h then convert all distance values to km and all time values to h before subbing them into the formula.

    Alternatively, you can do everything in m/s and then convert the final answer to km/h.
    • Political Ambassador
    • Thread Starter
    Offline

    20
    ReputationRep:
    (Original post by SeanFM)
    Use consistent units and you will get the answer in the same units.

    Eg if you were adding 5 hours to 40 minutes then you would not say t = 5 + 40. You would either convert 40 minutes to 2/3 hours to give t = 5 + 2/3, so you know that the answer is in hours, or alternatively t = 5*60 + 40, so you know that the answer is in minutes. As you have acceleration (already in m/s^2) you would need to be very careful as well. Best to stick to seconds for that reason.
    so im matching the time with the unit they use in acceleration? what about km/h?
    • Political Ambassador
    • Thread Starter
    Offline

    20
    ReputationRep:
    (Original post by BasicMistake)
    You need to use the same units throughout a calculation.

    If you are talking about km/h then convert all distance values to km and all time values to h before subbing them into the formula.

    Alternatively, you can do everything in m/s and then convert the final answer to km/h.
    so its best if i convert 72km/h into m/s? and then conver my final answer to km/h if they want it km/h?
    • Very Important Poster
    Online

    21
    ReputationRep:
    (Original post by ihatePE)
    so im matching the time with the unit they use in acceleration? what about km/h?
    I have just seen that the answer requires km/h so you may as well convert everything to that.
    • Political Ambassador
    • Thread Starter
    Offline

    20
    ReputationRep:
    (Original post by SeanFM)
    I have just seen that the answer requires km/h so you may as well convert everything to that.
    we all make mistakes :giggle: just to clarify i change the seconds to hours? what do i do about the acceleration thats in m/s?
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Break up or unrequited love?
    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

    Sponsored content:

    HEAR

    HEAR

    Find out how a Higher Education Achievement Report can help you prove your achievements.

    Groups associated with this forum:

    View associated groups
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • 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

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