Page 124 - Physics Coursebook 2015 (A level)

Cambridge International AS Level Physics
7 a
Figure 7.19 shows the stress–strain curves for three different materials, P, Q and R.
State and explain which material has the greatest Young modulus. [2]
P
Q R
00
Strain
Figure 7.19 For End-of-chapter Question 7.
b Describe an experiment to determine the Young modulus for a material in the form of a wire.
Include a labelled diagram and explain how you would make the necessary measurements.
Show how you would use your measurements to calculate the Young modulus. [7]
8 a
b A vertical steel wire of length 1.6 m and cross-sectional area 1.3 × 10−6 m2 carries a weight of 60 N.
State the meaning of tensile stress and tensile strain. [2]
The Young modulus for steel is 2.1 × 1011 Pa. Calculate:
i the stress in the wire [2]
ii the strain in the wire [2]
iii the extension produced in the wire by the weight. [2]
9 To allow for expansion in the summer when temperatures rise, a steel railway line laid in cold weather is pre-stressed by applying a force of 2.6 × 105 N to the rail of cross-sectional area 5.0 × 10−3 m2. If the railway line is not pre-stressed then a strain of 1.4 × 10−5 is caused by each degree Celsius rise in temperature. The Young modulus of the steel is 2.1 × 1011 Pa.
a State and explain whether the force applied to the rail when it is laid should be tensile or compressive. [2]
b Calculate:
i the strain produced when the rail is laid [3]
ii the temperature rise when the rail becomes unstressed. [2]
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Stress