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DP IB Physics: HL

Topic Questions

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2.2 Forces

Question 1a

Marks: 2

Curling is a game played on a horizontal surface of ice. A player pushes a large smooth stone across the ice for several seconds and then releases it. 

A 23.1 N force and 3.53 N force act on a stone of mass 19 kg at the same time. 

(a)
Calculate the magnitude of the maximum and minimum acceleration that can be experienced by the stone.
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    Key Concepts
    Newton's Second Law

    Question 1b

    Marks: 4

    The stone moves with a different set of forces until friction brings it to rest. The graph shows the variation of the stone’s speed with time.

    q1b_forces_ib-sl-physics-sq-medium

    The total distance travelled by the stone is 35.1 m. 

    (b)
    Determine the coefficient of dynamic friction between the stone and the ice during the last 13.0 s of the stone’s motion. 
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      Key Concepts
      Friction

      Question 1c

      Marks: 2

      The stone is now on an inclined plane at an angle θ to the horizontal where it is momentarily stationary.

      q1c_forces_ib-sl-physics-sq-medium

       

      (c)
      Label the diagram to show the forces acting on the stone that act parallel and perpendicular to the plane. Your answer should include the name, the direction and point of application of each force.
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        Question 1d

        Marks: 4

        The stone slowly starts to move down the slope. The coefficient of dynamic friction on the inclined plane is 10 % less than that on the flat surface. 

        (d)
        Determine the angle θ of the inclined plane to the horizontal.
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          Key Concepts
          Friction

          Question 2a

          Marks: 4

          Ric is standing in an elevator and has a mass of 68 kg. The elevator is moving upwards at a speed of 2.5 m s–1 and comes to rest 3.0 s later. 

          (a)
          Calculate the reaction force on Ric from the elevator floor during the time it takes the elevator to come to rest.
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            Key Concepts
            Newton's Second Law

            Question 2b

            Marks: 3

            Ric realises that he forgot his lab coat on the floor below. He again travels in the elevator which goes downwards at the same speed, coming to rest in the same time.    

            (b)
            Calculate the reaction force on Ric from the elevator floor during the time it takes to come to rest at the floor below.
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              Key Concepts
              Newton's Second Law

              Question 2c

              Marks: 2
              (c)
              Hence, deduce which deceleration period of the elevator would make Ric feel: 

              (i)         Lighter

              (ii)        Heavier

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                Question 2d

                Marks: 3

                In a serious stroke of bad luck, the elevator cable snaps and it falls freely. Ric experiences a sense of weightlessness. 

                (d)
                Explain, using appropriate laws of motion, why Ric feels a sense of weightlessness in this situation.
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                  Key Concepts
                  Newton’s Third Law

                  Question 3a

                  Marks: 3

                  Two blocks A and B are joined by a string and rest on a frictionless horizontal table. A force of 200N is applied horizontally on block B.

                  q3a_forces_ib-sl-physics-sq-medium

                    

                  (a)
                  Draw free–body diagrams for both boxes.
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                    Question 3b

                    Marks: 4

                    Block A has a mass of 3.0 kg and block B has a mass of 7.0 kg. 

                    (b)
                    Calculate the acceleration of each block and the tension in the string.
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                      Key Concepts
                      Newton's Second Law

                      Question 3c

                      Marks: 3

                      Block A is now placed on top of block B. The coefficient of static friction between the two blocks is 0.31. The bottom block is pulled with a horizontal force F.

                      q3c_forces_ib-sl-physics-sq-medium  

                      (c)
                      Draw free–body diagrams for both boxes.
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                        Question 3d

                        Marks: 4
                        (d)
                        Calculate the magnitude of the maximum force F that will result in both blocks moving together without slipping.
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                          Question 4a

                          Marks: 2

                          A mass is hung from two horizontal strings.

                          q4a_forces_ib-sl-physics-sq-medium

                           

                          (a)
                          Outline why the mass will not remain in equilibrium when attached to the strings in this way.
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                            Question 4b

                            Marks: 4

                            A flower pot of mass 15 kg hangs from two strings attached to the ceiling with tensions A and B, where it remains in equilibrium.

                            q4b_forces_ib-sl-physics-sq-medium  

                            (b)
                            Derive two equations for A in terms of B. Give any values to an appropriate number of significant figures.

                             

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                              Question 4c

                              Marks: 4
                              (c)

                              Hence, calculate tensions A and B.

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                                Question 4d

                                Marks: 2

                                A gardening enthusiast wants to hang a flower pot from two strings on the ceiling of their balcony. They have two pieces of string, but they are unfortunately quite old and frayed. 

                                (d)
                                Suggest and explain how they can attach the strings to the flower pot in order for them to stay intact.
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                                  Question 5a

                                  Marks: 2

                                  A stone block is pulled at constant speed up an incline by a cable attached to an electric motor.

                                  q5a_forces_ib-sl-physics-sq-medium 

                                  The incline makes an angle of 17º with the horizontal. The mass of the block is 180 kg and the tension T in the cable of 0.9 kN.

                                   

                                  (a)
                                  On the diagram draw and label arrows that represent the forces acting on the block.
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                                    Question 5b

                                    Marks: 4
                                    (b)
                                    State the type of friction in this system and calculate the frictional force.      
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                                      Key Concepts
                                      Newton's Second Law

                                      Question 5c

                                      Marks: 3
                                      (c)
                                      Hence, calculate the appropriate coefficient of friction.
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                                        Key Concepts
                                        Friction

                                        Question 5d

                                        Marks: 3

                                        The cable connecting the block to the electric motor abruptly breaks. 

                                        (d)
                                        Calculate the acceleration of the block.
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                                          Key Concepts
                                          Newton’s Second Law