Question 1. This question carries 24% of the marks for this assignment. Your answer to part (a) should be no more than about 300 words long. Show clearly each stage of your working for parts (b), (c) and (d).
(a).Explain how the mechanism illustrated in Figure 1 operates. Suggest a practical use for this particular mechanism.
Figure 1: An illustration of a mechanism
A rotating circular drive wheel contains a pin at its outer edge that engages one of four slots on the driven wheel.
The slots are located at 90 degrees to each other.
The drive wheel also has a raised semi-circular disc which is in contact with the driven wheel.
(b).After accelerating to a speed of 65 kph, a mine shaft lift which operates from a depth of 1800 metres raises its occupants to the surface. If the initial acceleration and final deceleration of the lift occurs over 80 metres, at the beginning and end of its travel, what was the total time of its ascent?
c. i.Find the angular velocity of the Earth:
- around its own axis in radians per second and degrees per second
- around the Sun in radians per second and degrees per day.
ii.If the average distance to the Sun from the Earth is about 150 000 000 km, calculate the tangential speed, in m s-1, of the Earth in the solar system.
(d).In science fiction films, it is common to see rotating space stations with artificial gravity. What angular velocity (in radians per second) would a cylindrical space station with a diameter of 500 metres need in order to create a centripetal acceleration for someone standing on the inside of the outer rim that is equal to the acceleration due to gravity on Earth?
Question 2. This question carries 26% of the marks for this assignment. Your answer should be no more than about 400 words. A car of mass 1200 kg is claimed to be capable of reaching a speed of 60 mph from rest in 8.3 seconds. Take 60 mph = 96 kph.
(a).Assuming that the rate of acceleration of the car is constant throughout the time it is accelerating, calculate the power that the engine of the car is developing at the wheels the moment before it reaches 60 mph.
(b).State two other assumptions that you made in order to arrive at your answer in part (a).
(c).Calculate the power used at 20 mph and at 40 mph, and from this information draw a graph of engine power output against speed.
(d).Calculate the total distance the car has travelled as it accelerates to 60 mph.
(e).If the effective cross-sectional area of the car is 1.9 m2, and its drag coefficient is 2.3, use your calculated power rating from part (a) to estimate the maximum speed the car could reach on level ground. Take the density of air to be 1.2 kg m-3.
Your answer will be marked according to the correctness of the method used, regardless of the value of engine power used in the calculation.
f.State two other assumptions that you made in order to arrive at your answer in part (e).
Question 3. This question carries 20% of the marks for this assignment. Show clearly each stage of your calculations and working. For a particular car windscreen wiper mechanism, an electric motor is required that can provide 5 N m of torque at about 35 rpm. A small permanent magnet d.c. motor is suggested as being suitable for this purpose. The manufacturer's data is as follows:
Stall torque: 0.15 N m
Stall current: 15 A
No-load speed: 6000 rpm
No-load current: 0.5 A
Supply voltage: 12 V
Show that this motor has the power to do the job, and determine an approximate gear ratio with which it should be used in order to supply the necessary combination of torque and speed. You can either follow the overall approach adopted in Section 4.7 of Block 3 Part 3, adapting the working to the present needs, or put the data into the Mathcad sheet ‘Selecting a d.c. motor' and copy one or more of the graphs into your answer to show how you solved the problem. Provide a commentary as necessary.
Note: if you need to change the maximum or minimum value of the axis of a graph in Mathcad, click on the graph and you will see the values set for maxima and minima. Click on the one to be changed and use the delete key and other keys to set a new value; then click outside the frame of the graph.
Question 4. This question carries 22% of the marks for this assignment. In total, your answer should be no more than about 750 words long.
(a) Identify three factors that might be scrutinised by a team of engineering innovators who are seeking scope for commercial advantage in the design of a new airliner. Briefly justify why you identified each of the three factors.
(b).Bending and torsion are the main loading modes that the wings of conventional aeroplanes are subjected to during flight.
i. Describe, with the aid of simple sketches, the main causes of bending and torsion in wings when the aeroplane is cruising on a level flight path.
ii.Discuss how a commercial aeroplane wing structure, designed for minimum weight, has evolved to resist the service loads you described in part (b)(i).