Join TSR now and get all your revision questions answeredSign up now

Mechanics 1 help

    • Thread Starter
    Online

    3
    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)
    Online

    3
    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

    3
    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.
    • Thread Starter
    Online

    3
    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?
    • Thread Starter
    Online

    3
    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?
    Online

    3
    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.
    • Thread Starter
    Online

    3
    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?
 
 
 
Poll
Do you have exam superstitions?
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

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.