Quizzes > Engp Q3 02

UNIVERSITY OF SOUTH AUSTRALIA Applied Physics - School of Electrical & Information Engineering ENGINEERING PHYSICS QUIZ 3 [ week 7 ] Time: 20 minutes

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

QUESTIONS ( 8 MARKS )

Marks: 17/15

ANSWERS

1. Consider a point on a bicycle wheel as the wheel turns about a fixed axis, neither speeding up nor slowing down. Compare the linear acceleration a and the angular acceleration α of the point? A. Both are zero. B. Only the angular acceleration is zero. C. Neither are zero. D. Only the linear acceleration is zero.

2. The prefix pico represents … A. B. C. D.

10-10, 10-12, 10-15, 10-9.

3. You are the science officer on board the starship Enterprise and you are called upon to interpret sensor readings that show a planet to have a mass that is 4.0 times the Earth mass and a radius that is 3.0 times as large as the Earth radius. Before you beam an ‘away team’ to the surface you need to calculate the gravitational field they will experience. At its surface, this planet could be expected to have an acceleration due to gravity of … A. 0.44 times that on the surface of the Earth, B. 0.75 times that on the surface of the Earth, C. approx. 1.33 times that on the surface of the Earth, D. not even Spock can calculate that one, insufficient information.

4. In mechanical equilibrium, an object must have … A. B. C. D.

a constant velocity, zero acceleration, zero total force acting on it, all of the above.

5. If a uniform, heavy cable is suspended from one end, the cable is most apt (likely) to break from its own weight at a point … A. near its top end where it is suspended, B. near its bottom end, C. near the middle, D. anywhere along its length.

6. Astronauts in spacecraft on the way to the moon or orbiting the earth have been described as being in a “weightless” or “zero-g” condition because … A. they have no mass at this point, B. they are beyond the range of the Earth’s gravity, C. both they and their spacecraft move and accelerate together, D. the spacecraft is covered with a special alloy which that does not allow the gravitational field to penetrate, E. this is all done with trick photography as part of a massive plot by the bilateral commissars and their puppet press.

7. You are coming in to land your Kendell’s Airlines aircraft at Adelaide airport and hit a seagull flying in the opposite direction square in the middle of the pilot’s front window. Without all the gruesome details, the bird sadly was deceased and the window remained intact. We then know that, A. the force of the bird on the glass was bigger than the force of the glass on the bird, B. the force of the bird on the glass was the same as the force of the glass on the bird, C. the force of the bird on the glass was less than the force of the glass on the bird, D. the aircraft didn’t slow down as it hit the bird.

PROBLEMS ( 10 MARKS ) Question 1 (4 marks) A person is skiing down a wet Australian snow covered slope (indicated by the dashed line), lucky them. Briefly describe all the forces acting on the person and identify the ‘reaction’ force corresponding to each. Indicate the forces on the diagram. [Remember to identify where the vectors act and their relative magnitudes are indicated by the length of the vectors/arrows.] ………………………………………..………………………………… ………………………………………..………………………………… ………………………………………..………………………………… ………………………………………..………………………………… ………………………………………..………………………………… ………………………………………..………………………………… ………………………………………..………………………………… ………………………………………..………………………………… ………………………………………..…………………………………

Problem 1 (6 marks) A compact disk (CD) is 6.00cm in radius and has a moment of inertia of 1.6 x 10-6 kg.m2 and rotates at a constant rate of 1200 revolutions per minute about its central axis. {Hint: s, v, a, θ, ω, α} (i) Determine its angular speed. [2 marks]

1 ………………………………………..…………………………………………………………………………… s = v0 t +

at 2

2 ………………………………………..……………………………………………………………………………

v f = v 0 + at ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… v 2f = v 02 + 2as ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… (ii) What is the linear speed of a point on the rim of the disk?. [2 marks] ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… (iii) What is the magnitude and direction of the linear acceleration of a point on the rim?. Indicate the direction on the diagram below. [2 marks] ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..……………………… ………………………………………..……………………… ………………………………………..……………………… ………………………………………..……………………… ………………………………………..………………………