Hey! Sign in to get help with your study questionsNew here? Join for free to post

M1 q.

Announcements Posted on
International student planning UK study in 2016? Take our short survey and we’ll send you a £5 Amazon voucher 03-05-2016
Talking about ISA/EMPA specifics is against our guidelines - read more here 28-04-2016
  1. Offline

    ReputationRep:
    A ball is projected upwards from a point which is 4m above the ground with speed 18ms^-1 find:

    a)The speed of the ball when it is 15m above its point of projection
    b)The speed with which the balls hits the ground

    So I drew a diagram and I tried to attempt this question a different way than what the book did:



    I ignored the red particle and started from the green:

    from the green I said u = 0, a = 9.8 and s = 19 and found the velocity to be 19.29

    I then done it another way with u = 18, a = -9.8 and s = -4 and I get the velocity to be about 20ms^-1

    these two are very similar so im not sure whats going wrong

    EDIT: I realised that for some reason i'm assuming that the 15m is its maximum distance, is this why they are different?
  2. Offline

    (Original post by thorn0123)
    EDIT: I realised that for some reason i'm assuming that the 15m is its maximum distance, is this why they are different?
    Yes. At 15m its speed is 5.48 m/s (3 sig.fig.)
  3. Offline

    ReputationRep:
    (Original post by thorn0123)
    A ball is projected upwards from a point which is 4m above the ground with speed 18ms^-1 find:

    a)The speed of the ball when it is 15m above its point of projection
    b)The speed with which the balls hits the ground

    So I drew a diagram and I tried to attempt this question a different way than what the book did:



    I ignored the red particle and started from the green:

    from the green I said u = 0, a = 9.8 and s = 19 and found the velocity to be 19.29

    I then done it another way with u = 18, a = -9.8 and s = -4 and I get the velocity to be about 20ms^-1

    these two are very similar so im not sure whats going wrong

    EDIT: I realised that for some reason i'm assuming that the 15m is its maximum distance, is this why they are different?
    Your thinking is correct, 15m isn't the max distance.

    You have assumed the speed to be zero when the particle is 19m above the ground, while this is not the case, its speed at that instant is  \sqrt{30}

    EDIT: Beaten to it!
  4. Offline

    ReputationRep:
    (Original post by thorn0123)
    A ball is projected upwards from a point which is 4m above the ground with speed 18ms^-1 find:

    a)The speed of the ball when it is 15m above its point of projection
    b)The speed with which the balls hits the ground

    So I drew a diagram and I tried to attempt this question a different way than what the book did:



    I ignored the red particle and started from the green:

    from the green I said u = 0, a = 9.8 and s = 19 and found the velocity to be 19.29

    I then done it another way with u = 18, a = -9.8 and s = -4 and I get the velocity to be about 20ms^-1

    these two are very similar so im not sure whats going wrong

    EDIT: I realised that for some reason i'm assuming that the 15m is its maximum distance, is this why they are different?

    a) The mistake you made here was to assume that S is the distance from the ground, it isn't, it is the displacement.

    S= 15
    U=18
    V=To be found <--Up is positive
    A=-9.8
    T=Unknown

    V^2=U^2+2as
    V^2=294
    V=17.1ms-1

    b)

    S=-4
    U=18
    V=To be found <---upwards is positive
    A=-9.8
    T=Unknown

    V^2=U^2+2as
    V^2=402.4
    V=20.1ms-1


    I hope my calculations are right, I used a pathetic calculator on my computer!
  5. Offline

    ReputationRep:
    (Original post by SpiggyTopes)
    a) The mistake you made here was to assume that S is the distance from the ground, it isn't, it is the distance travelled.
    Actually, both answers were for part (b)... And if something goes up, comes down, and hits the ground, S is the distance from the ground, not distance traveled.
  6. Offline

    ReputationRep:
    (Original post by aznkid66)
    Actually, both answers were for part (b)... And if something goes up, comes down, and hits the ground, S is the distance from the ground, not distance traveled.
    I'm sorry, I meant displacement! Schoolboy error!

Reply

Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. Oops, you need to agree to our Ts&Cs to register
  2. Slide to join now Processing…

Updated: June 30, 2012
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Today on TSR

CIE maths exam

How did it go?

Poll
How often are people with Asthma hospitalised in the UK?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read here first

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