Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    2
    ReputationRep:
    A stone falls down a well vertically. Ignore friction.

    it falls 60m , initial speed = 5m/s

    acceleration must be -9.8m/s/s

    If i use s = ut +1/2at^2 I can get an answer but it comes out as

    -60 = 5t - 4.9t^2

    I'm fairly sure you shouldn't have to use quadratic formula for a short question. What's wrong?
    Offline

    19
    ReputationRep:
    What's the issue with using the quadratic formula?

    You've messed up a sign btw.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by alow)
    What's the issue with using the quadratic formula?

    You've messed up a sign btw.
    got the mistake.My point was is there a different way
    Offline

    19
    ReputationRep:
    (Original post by Feynboy)
    which one?
    If you're saying the fall is in the -ve direction, what is your starting velocity?
    Offline

    17
    ReputationRep:
    The quadratic form would be
    0 = - 4.9t^2 + 5t + 60
    Offline

    12
    ReputationRep:
    (Original post by Feynboy)
    A stone falls down a well vertically. Ignore friction.

    it falls 60m , initial speed = 5m/s/s

    acceleration must be -9.8m/s/s

    If i use s = ut +1/2at^2 I can get an answer but it comes out as

    -60 = 5t - 4.9t^2

    I'm fairly sure you shouldn't have to use quadratic formula for a short question. What's wrong?
    Acceleration is positive if it's falling down. The equation should be:-
    4.9t^2 + 5t-60=0.
    Offline

    19
    ReputationRep:
    (Original post by sabahshahed294)
    Acceleration is positive if it's falling down. The equation should be:-
    4.9t^2 + 5t-60=0.
    Not if you take upwards as +ve. As long as you're consistent it can be either way.
    Offline

    12
    ReputationRep:
    (Original post by alow)
    Not if you take upwards as +ve. As long as you're consistent it can be either way.
    You mean the displacement right? Because if a=g here then a is positive.
    Offline

    19
    ReputationRep:
    (Original post by sabahshahed294)
    You mean the displacement right? Because if a=g here then a is positive.
    I mean taking upwards as being +ve displacement, like OP has done.
 
 
 
  • 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
    Brussels sprouts
  • 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.