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

    4
    ReputationRep:
    Hi so i know how to work out nmomentum using the original formula (momentum=mass x velocity) and i can re arrange
    but im stuck on working out momentum after a collision and velocity after a collision
    etc

    A 0.5kg trolley A is pushed at a velocity of 1.2m/s into a stationary trolley B of mass 1.5kg. The two trolleys stick to each other after the impact. What is the momentum of trolley A before the collision. What is the velocity of the two trolleys after the collision?


    can anyone help?
    Also how do you use the conservation of momentum when working out using equations/formulas?
    thanks
    Offline

    0
    ReputationRep:
    A 0.5kg trolley A is pushed at a velocity of 1.2m/s into a stationary trolley B of mass 1.5kg. The two trolleys stick to each other after the impact. What is the momentum of trolley A before the collision. What is the velocity of the two trolleys after the collision?
    Total momentum before=0.5*1.2+1.5*0=0.6 kgm/s
    Total momentum after=total energy before (by conservation of linear momentum)
    So Total momentum after= 0.6 =(0.5+1.5)*v
    So v=0.6/2=0.3 m/s
    Offline

    0
    ReputationRep:
    I got 0.3m/s as my answer
    Offline

    9
    ReputationRep:
    (Original post by XShmalX)
    A 0.5kg trolley A is pushed at a velocity of 1.2m/s into a stationary trolley B of mass 1.5kg. The two trolleys stick to each other after the impact. What is the momentum of trolley A before the collision. What is the velocity of the two trolleys after the collision?
    Total energy before=0.5*1.2+1.5*0=0.6 kgm/s
    Total energy after=total energy before (by conservation of linear momentum)
    So Total energy after= 0.6 =(0.5+1.5)*v
    So v=0.6/2=0.3 m/s
    All of the maths here is correct, and has lead to the right answer. Do note though that we are talking about momentum rather than energy; they are quite different. Replace every instance of "energy" with "momentum" and it's perfect!
    Offline

    13
    ReputationRep:
    (Original post by halii_94)
    Hi so i know how to work out nmomentum using the original formula (momentum=mass x velocity) and i can re arrange
    but im stuck on working out momentum after a collision and velocity after a collision
    etc

    A 0.5kg trolley A is pushed at a velocity of 1.2m/s into a stationary trolley B of mass 1.5kg. The two trolleys stick to each other after the impact. What is the momentum of trolley A before the collision. What is the velocity of the two trolleys after the collision?


    can anyone help?
    Also how do you use the conservation of momentum when working out using equations/formulas?
    thanks
    For future reference, when the trolleys stick to each other you can take their masses as one mass.
    Offline

    0
    ReputationRep:
    (Original post by Pangol)
    All of the maths here is correct, and has lead to the right answer. Do note though that we are talking about momentum rather than energy; they are quite different. Replace every instance of "energy" with "momentum" and it's perfect!
    doh! Having a totally brainstorm!
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by XShmalX)
    A 0.5kg trolley A is pushed at a velocity of 1.2m/s into a stationary trolley B of mass 1.5kg. The two trolleys stick to each other after the impact. What is the momentum of trolley A before the collision. What is the velocity of the two trolleys after the collision?
    Total momentum before=0.5*1.2+1.5*0=0.6 kgm/s
    Total momentum after=total energy before (by conservation of linear momentum)
    So Total energy after= 0.6 =(0.5+1.5)*v
    So v=0.6/2=0.3 m/s
    why do you divide it by 2 if the velocity is 1.2m/s?
    Offline

    0
    ReputationRep:
    (Original post by halii_94)
    why do you divide it by 2 if the velocity is 1.2m/s?
    The total initial momentum is calculated by multiplying the mass of each trolley by its velocity.
    The momentum before must equal the total momentum after by conservation of momentum.
    So as the two trolleys stick together the momentum is divided by the totally mass of the two trolleys stuck together in order to find the velocity.
    Offline

    13
    ReputationRep:
    (Original post by halii_94)
    why do you divide it by 2 if the velocity is 1.2m/s?
    Momentum of A = mass x velocity
    = 0.5 x 1.2
    = 0.6kgm/s (momentum)

    Momentum before collision = momentum after the collision

    0.6 = mass of the two trolleys combined (says they stick) x velocity of trollies.

    0.6 = 2 x Velocity

    Velocity = 0.3m/s
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by XShmalX)
    The total initial momentum is calculated by multiplying the mass of each trolley by its velocity.
    The momentum before must equal the total momentum after by conservation of momentum.
    So as the two trolleys stick together the momentum is divided by the totally mass of the two trolleys stuck together in order to find the velocity.
    so if there were 3 etc trolleys it would divide by 3?
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by gozatron)
    Momentum of A = mass x velocity
    = 0.5 x 1.2
    = 0.6kgm/s (momentum)

    Momentum before collision = momentum after the collision

    0.6 = mass of the two trolleys combined (says they stick) x velocity of trollies.

    0.6 = 2 x Velocity

    Velocity = 0.3m/s
    thank you
    Offline

    0
    ReputationRep:
    (Original post by halii_94)
    so if there were 3 etc trolleys it would divide by 3?
    No you'd divide by the sum of the masses of the three trolleys. It just happens that in this case the two mass are 0.5 kg and 1.5 kg and so equal 2 kg.
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by XShmalX)
    No you'd divide by the sum of the masses of the three trolleys. It just happens that in this case the two mass are 0.5 kg and 1.5 kg and so equal 2 kg.
    thank youu
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by XShmalX)
    No you'd divide by the sum of the masses of the three trolleys. It just happens that in this case the two mass are 0.5 kg and 1.5 kg and so equal 2 kg.
    one last thing

    A car of mass 950kg is travelling at 20m/s when it shunts a car of mass 1000kg which is travelling at 15m/s
    what is the velocity of the two cars after the collision?

    i got the answer 17.44 m/s
    does that sound right?
    thanks a lot
    Offline

    0
    ReputationRep:
    (Original post by halii_94)
    one last thing

    A car of mass 950kg is travelling at 20m/s when it shunts a car of mass 1000kg which is travelling at 15m/s
    what is the velocity of the two cars after the collision?

    i got the answer 17.44 m/s
    does that sound right?
    thanks a lot
    Assuming they are traveling at the same speed, but otherwise the question wouldn't be possible, so yes!
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by XShmalX)
    Assuming they are traveling at the same speed, but otherwise the question wouldn't be possible, so yes!
    yay thanks you it has taken me months literally to understand momentum lol
 
 
 
  • 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
    Did TEF Bronze Award affect your UCAS choices?
  • 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.