Elasticity and Hooke's lawIB MYP Physics: Subtopic test

1. 1
   A trampoline manufacturer in Melbourne joins the mat to the frame with steel springs. Each spring has a natural length of 20 cm. In a test, a weight of 12 N is hung from one spring and its length becomes 26 cm. The spring is not stretched beyond its limit of proportionality.

   (a)

   What is the extension of the spring when the 12 N weight is hung from it?

   [1 mark]

   • A26 cm
   • B20 cm
   • C6 cm
   • D32 cm

   (b)

   What is the spring constant of the spring?

   [1 mark]

   • A200 N/m
   • B2 N/m
   • C72 N/m
   • D0.005 N/m

   (c)

   The same spring is stretched by a weight of 18 N. Calculate the extension in cm.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A workshop technician in Kuala Lumpur tests a steel spring by hanging increasing loads from it. Up to 15 N the extension is directly proportional to the load and the spring returns to its original length when the load is removed. A load of 25 N takes the spring beyond its elastic limit.

   (a)

   What is meant by the limit of proportionality of a spring?

   [1 mark]

   • AThe force at which the spring breaks
   • BThe force at which the spring stops stretching
   • CThe extension at which the spring first returns to its original length
   • DThe largest force for which the extension is directly proportional to the force

   (b)

   Which describes what happens to the spring when the 25 N load is applied and then removed?

   [1 mark]

   • AElastic deformation, because the spring stretched
   • BPlastic deformation, because the spring does not return to its original length
   • CNo deformation, because the spring still works
   • DElastic deformation, because the extension was proportional to the load

   (c)

   Explain what happens to the length of the spring after (i) a 10 N load is removed and (ii) the 25 N load is removed.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student in Vancouver hangs loads from a spring and measures the extension each time. A 2.0 N load gives an extension of 4.0 cm, a 4.0 N load gives 8.0 cm, a 6.0 N load gives 12.0 cm, an 8.0 N load gives 16.0 cm and a 10.0 N load gives 22.0 cm.

   (a)

   Calculate the spring constant of the spring in N/m using the first four results.

   [3 marks]

   (b)

   Describe the pattern in the results and use it to decide where the limit of proportionality lies. State what the gradient of the straight part of a force-extension graph would represent.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A toy company in Shenzhen is choosing between a steel spring and a rubber band for the launcher of a toy catapult for children. Both store energy when stretched. An engineer knows that a steel spring obeys Hooke's law up to a limit, but a rubber band may behave differently, and she tests both in the laboratory using a clamp stand, a metre rule and 1 N weights.

   (a)

   The engineer's hypothesis is that the extension of a rubber band is directly proportional to the load hung from it. Describe an investigation to test this hypothesis, including the variables you would control and how you would analyse the results.

   [6 marks]

   (b)

   Discuss and evaluate whether the company should use a steel spring or a rubber band in its toy launcher.

   [6 marks]

   Total for question 4: 12 marks

End of questions