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DP IB Physics: HL

Topic Questions

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2.4 Momentum & Impulse

Question 1a

Marks: 2

(a)

(i)
Write an equation for the momentum of an object in words
[1]
(ii)
State the fundamental SI units of momentum
[1]

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    Key Concepts
    Force & Momentum

    Question 1b

    Marks: 3

    A railway carriage, C1, of mass 1100 kg is rolling along a horizontal track at a speed of 6 m s−1 towards a stationary carriage, C2, as shown below. Carriage C2 has a mass of 3300 kg.

    question-1b-figure-1

    (b)
    Calculate:

    (i)
    The initial momentum of carriage C1 before the collision
    [2]
    (ii)
    The initial momentum of carriage C2 before the collision.
    [1]
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      Key Concepts
      Force & Momentum

      Question 1c

      Marks: 3

      At the moment of collision, both carriages C1 and C2, become joined.

      The joined carriages move off with a velocity, v, as shown below.

      question-1c-figure-2

      (c)
      Calculate the total momentum of C1 and C2 after they have joined.
      Use your answers from part (b) and the conservation of momentum. 

       [3]

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        Question 1d

        Marks: 3
        (d)
        Calculate the velocity, v, at which the carriages C1 and C2 move after becoming joined.
        [3]
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          Question 2a

          Marks: 3

          A film stuntman, of mass 85.0 kg, is being trained to jump off high objects. 

          In one scene he steps off a roof and falls vertically to the ground below. Just before he hits the ground he has a velocity of 9.08 m s−1. After he has landed on the ground he remains at rest.

          (a)
          Calculate the momentum of the stuntman:

          (i)
          Just before he hits the ground.
          [2]
          (ii)
          After he has landed.
          [1]

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            Key Concepts
            Force & Momentum

            Question 2b

            Marks: 2
            (b)
            Using your answers to part (a), calculate the change of momentum of the stuntman during the landing.
            [2]
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              Key Concepts
              Impulse

              Question 2c

              Marks: 2
              (c)
              State the impulse experienced by the stuntman during landing.
              Give an appropriate unit with your answer.
              [2]
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                Question 2d

                Marks: 4

                When the stuntman keeps his legs fully rigid, the time for the impact is 4.20 ms. 

                (d)
                Calculate the magnitude of the average resultant force acting on the stuntman’s legs during this time.
                [4]
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                  Key Concepts
                  Impulse in Context

                  Question 3a

                  Marks: 2

                  A bullet, of mass 20 g, leaves the barrel of a rifle, of mass 1.9 kg, with a momentum 4.0 kg m s−1.

                  (a)
                   
                  (i)
                  State the total momentum of the rifle and the bullet before the rifle is fired
                  [1]
                  (ii)
                   Give a reason for your answer to part (i)
                  [1]
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                    Question 3b

                    Marks: 3
                    (b)
                    Calculate the velocity of the bullet just after the rifle is fired.
                    [3]
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                      Key Concepts
                      Force & Momentum

                      Question 3c

                      Marks: 4
                      (c)
                      Use the principle of conservation of momentum and your answer to part (a) to:

                      (i)
                      State the total momentum of the rifle and the bullet immediately after the rifle has been fired.
                      [2]
                      (ii)
                      Calculate the recoil momentum of the rifle.
                      [2]

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                        Question 3d

                        Marks: 4

                        The bullet has a momentum of 3 kg m s−1 just before it hits a target. It takes 0.0025 s for the bullet to be stopped by the target. 

                        bold italic F bold space bold equals bold space fraction numerator bold increment bold italic p over denominator bold increment bold italic t end fraction

                        (d)
                        Calculate the average force needed to stop the bullet.
                        [4]
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                          Key Concepts
                          Impulse

                          Question 4a

                          Marks: 6

                          Zorbing is an activity which involves a person running inside an inflatable ball, called a ‘zorb’.  Two zorbs, A and B, collide head on with each other, as shown.  The total mass of zorb A and its occupant is 75 kg and the total mass of zorb B and its occupant is 60 kg.  Before the collision, zorb A is travelling at 2.0 m s−1 and zorb B is travelling at 1.5 m s−1.

                          new-q4a

                          (a)
                          Calculate:

                          (i)
                          The momentum of zorb A before the collision
                          [2]
                          (ii)
                          The momentum of zorb B before the collision
                          [2]
                          (iii)
                          The total momentum of both zorbs before the collision  
                          [2]

                             

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                            Key Concepts
                            Force & Momentum

                            Question 4b

                            Marks: 6

                            After the collision, both zorbs bounce off each other and move in opposite directions, as shown below. Zorb A travels at 0.8 m s−1 and zorb B travels at 2.0 m s−1.

                            new-q4b

                            (b)
                            Calculate:

                            (i)
                            The momentum of zorb A after the collision
                            [2]
                            (ii)
                            The momentum of zorb B after the collision
                            [2]
                            (iii)
                            The total momentum of both zorbs after the collision
                            [2]
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                              Key Concepts
                              Force & Momentum

                              Question 4c

                              Marks: 4
                              (c)
                              Calculate:

                              (i)
                              The total kinetic energy of the zorbs before the collision.
                              [2]
                              (ii)
                              The total kinetic energy of the zorbs after the collision.
                              [2]

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                                Question 4d

                                Marks: 3
                                (d)
                                State whether: 

                                (i)
                                Momentum is or is not conserved during the collision of the zorbs.
                                [1]
                                (ii)
                                Kinetic energy is or is not conserved during the collision of the zorbs.
                                [1]
                                (iii)
                                The collision of the zorbs is elastic or inelastic.
                                [1]
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                                  Question 5a

                                  Marks: 3

                                  A collision can be described as being elastic or inelasticWhen there are no external forces acting on the collision.

                                  (a)
                                  Place a tick (✓) next to the quantities that are conserved in each type of collision, 

                                   

                                  Quantity

                                  Elastic Collision

                                  Inelastic Collision

                                  Momentum

                                     

                                  Total Energy

                                     

                                  Kinetic Energy

                                     

                                  [3] 

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                                    Question 5b

                                    Marks: 2

                                    During a safety test, a car of mass 1250 kg travels at 0.5 m s−1 towards a wall.

                                    (b)
                                    Calculate the momentum of the car before it collides with the wall.
                                    [2]
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                                      Key Concepts
                                      Impulse in Context

                                      Question 5c

                                      Marks: 3

                                      The car has a force sensor attached to the bumper which detects the force exerted on the front of the car.  The graph below shows the variation of force with time for the duration of the collision.

                                      2-4-5c-q-sl-sq-easy-phy

                                      (c)
                                      Use the graph to show that the impulse of the collision is 625 N s. 
                                      [3]
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                                        Key Concepts
                                        Impulse

                                        Question 5d

                                        Marks: 2

                                        All cars are designed with a crumple zone to protect passengers if they are involved in a collision.

                                        (d)
                                        State how a crumple zone:

                                        (i)
                                        Affects the impact time of a collision.
                                        [1]
                                        (ii)
                                        Affects the force exerted on the car during a collision.
                                        [1]

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                                          Key Concepts
                                          Impulse in Context