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UNIVERSITY OF SOUTH AUSTRALIA School of Electrical & Information Engineering (Applied Physics) ENGINEERING PHYSICS QUIZ 3 [ week 13 ] Time: 20 minutes

Name .....................................................................................

QUESTIONS ( 8 MARKS )

Marks: 20 ANSWERS

1. If the net external torque on a rigid body about some origin is zero, it means that A. B. C. D.

the angular momentum of the rigid body about the origin is constant, the angular acceleration of the rigid body about the origin is zero, the angular speed of the rigid body about the origin is constant all of the above are true.

2. Which of the following is incorrect? A. B. C. D.

An elastic collision is when the total kinetic energy of the system is conserved. A perfectly elastic collision is one in which the colliding bodies stick together after collision. Momentum is always conserved. An inelastic collision is one in which the total kinetic energy of the system is not conserved.

3. A karate expert executes a swift blow and breaks a cement block with a bare hand. The magnitude is the same for A. B. C. D.

the impulse on both the block and the expert’s hand, the time of impact on both the block and the expert’s hand, the force on both the block and the expert’s hand, all of the above

4. What does a scanning tunneling microscope measure? A. B. C. D. E.

electrons electron density of states electron probability all of the above none of the above

5. Isotopes of an element contain A. B. C. D. E.

the same number of neutrons but a different number of electrons the same number of electrons but a different number of protons the same number of neutrons but a different number of protons the same number of nucleons none of the above

6. An external observer sees a person on a moving train shine a torch at the floor of the train. A. B. C. D. E.

From the external observers’ point of view the light travels a longer distance than the person on the train observes. faster than the person on the train observes. a shorter distance than the person on the train observes. slower than the person on the train observes. none of the above.

7. The spectral distribution shown exhibits characteristic x-ray peaks. These arise from… electron interaction with the nucleus core level ionisation photon absorption all of the above none of the above

8. The emission of radiation from an atom or molecule arises from A. B. C. D. E.

the vibration of the molecular bonds the transition of an electron between energy levels the rotation of a molecule all of the above none of the above

Intensity

A. B. C. D. E.

Wavelength

QUESTIONS & PROBLEMS ( 14 MARKS ) Question 1 (4 marks) Explain the difference between alpha, beta and gamma particles and how one could distinguish them apart experimentally. Discuss properties such as charge, mass and relative penetrating power. ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… Problem 1 (5 marks) A disk 8.00 cm in radius and with a moment of inertia of 1.6 x 10–3 kg.m2 rotates at a constant rate of 1200 revolutions per minute about its central axis. Determine (a) its angular speed in SI units (1 mark), (b) the linear speed of a point on the rim of the disk (1 mark), (c) the magnitude and direction of the linear acceleration of a point on the rim (1 mark), (d) the angular acceleration of the disk (1mark), and (e) the rotational kinetic energy of the disk (1 mark). ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… Problem 2 (5 marks) A car traveling at the speed limit (60km/hr) north along Main North Rd reaches the traffic lights at Grand Junction Rd. While traveling through the intersection it is hit by another car traveling east along Grand Junction Rd. The cars stick together after collision and continue with a final speed of 10km/hr along Main North Rd (which makes an angle of 45° with Grand Junction at the intersection. i.e. NE direction). Draw a diagram of this situation (2 marks). What is the initial speed of the car traveling along Grand Junction Rd? (3 marks) ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ………………………………………………………………………………………