Stress, strain and the Young modulusEdexcel International A Level Physics: Mind map

Exam questions on Stress, strain and the Young modulus

1. A steel wire of original length 2.50 m and diameter 0.80 mm hangs vertically from a rigid support. A load of 120 N is attached to the lower end of the wire and the wire extends by 3.0 mm. The wire obeys Hooke's law.
   Calculate the Young modulus of the steel.2 marks
2. A ductile metal wire of cross-sectional area 2.0 × 10⁻⁷ m² is stretched until it breaks. The stress is directly proportional to the strain up to a stress of 2.4 × 10⁸ Pa, and the wire breaks when the stress reaches 3.6 × 10⁸ Pa.
   A second wire is made of the same metal but has twice the diameter. State and explain how its breaking stress and the force needed to break it compare with the first wire.2 marks
3. A student determines the Young modulus of a copper wire. One end of the wire is clamped to a bench and the wire passes over a pulley, with masses added to the free end. The original length of the wire, measured from the clamp to a marker with a metre rule, is 2.00 m. The mean diameter of the wire, measured with a micrometer screw gauge, is 0.50 mm. The student plots a graph of force against extension, which is a straight line through the origin of gradient 1.2 × 10⁴ N m⁻¹.
   Explain why the student uses a long, thin wire.3 marks