Resultant force and vectorsIB MYP Physics: Subtopic test

1. 1
   A delivery cyclist in Nairobi rides 6 km east along a straight road, then turns and rides 8 km north to reach a school. The whole journey takes 40 minutes.

   (a)

   Which one of these quantities is a vector?

   [1 mark]

   • AThe displacement of the cyclist from her starting point
   • BThe total distance she travels
   • CThe time her journey takes
   • DThe mass of the cyclist

   (b)

   What is the size of the cyclist's displacement from her starting point at the end of the journey?

   [1 mark]

   • A14 km
   • B2 km
   • C10 km
   • D48 km

   (c)

   Explain why the size of the cyclist's displacement is different from the distance she travels.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Two workers in a warehouse in Lagos push a heavy crate along a smooth floor. Friction between the crate and the floor is so small that it can be ignored. One worker pushes to the right with a force of 300 N and the other pushes to the left with a force of 220 N.

   (a)

   What is the resultant force on the crate?

   [1 mark]

   • A520 N to the right
   • B80 N to the left
   • C300 N to the right
   • D80 N to the right

   (b)

   Which statement describes the motion of the crate?

   [1 mark]

   • AIt stays at rest
   • BIt accelerates to the right
   • CIt moves at constant velocity to the right
   • DIt accelerates to the left

   (c)

   A third worker joins and also pushes to the left, with a force of 80 N. The crate is moving to the right at that moment. Calculate the new resultant force and describe how the crate's motion now changes.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student in Seoul is finding out how two forces at right angles combine. She fixes a small metal ring to a flat board. Two newton meters pull the ring at right angles to each other, and a third newton meter pulls in the opposite direction to the resultant of the first two so that the ring stays at rest.

   (a)

   She pulls the ring with forces of 6.0 N and 8.0 N at right angles to each other. Calculate the reading on the third newton meter when the ring is at rest.

   [3 marks]

   (b)

   The student's hypothesis is: "The resultant of two forces at right angles is equal to the sum of the two forces." Evaluate this hypothesis using your answer to (a).

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A construction company in Mumbai uses a tower crane to lift steel beams. When a beam hangs still from the cable it is in equilibrium. The company's engineers worry that wind or a faulty cable could make a hanging beam swing or drop. In the laboratory, a technician models the crane with a newton meter hanging from a clamp stand and a set of small masses.

   (a)

   The technician hypothesises that when a mass hangs at rest from the newton meter, the reading equals the weight of the mass. Describe a safe investigation to test this hypothesis. Weight = mass × 10 N/kg. Include the variables you would control.

   [6 marks]

   (b)

   The company is considering fitting sensors to its crane cables. A sensor sounds an alarm if the upward pull of the cable becomes different from the weight of the load, because the load is then no longer in equilibrium and may be swinging or dropping. Discuss and evaluate whether the company should fit the sensors to all of its cranes.

   [6 marks]

   Total for question 4: 12 marks

End of questions