Self Test on Tutorial 8
Answer these multiple choice questions:
1. An aeroplane is in level flight at constant speed. Which one line shows the correct pairing of forces to achieve this?
2. Which one of these factors does drag acting on an object NOT depend on?
A: Mass of the object;
C: Density of the fluid;
D: Shape of the object.
3. A light aircraft of mass 900 kg is held in the air by a pressure difference of about 6 millibars. What should the surface area of the wing be? 1 bar = 1.013 ◊ 105 N m-2.
A: 1.48 m2;
B: 14.5 m2;
C: 150 m2;
D: 1.47 ◊ 106 m2.
4. Which one of these accurately describes what happens when an aircraft stalls?
A: The pilot lets the clutch up too quickly so the engine stops;
B: The aeroplane has run out of petrol;
C: Air has stopped flowing around the wing, piling up at the front and pushes the wing down;
D: The air flow above the wing becomes turbulent due to a high angle of attack. This reduces the lift.
5. How is the force due to drag related to speed?
A: It is not related at all;
B: It is related to speed;
C: It is related to velocity;
D: It is related to the square of the speed.
6. A designer of an aeroplane replaces a piston engine of 150 kW by a gas turbine of 300 kW. What will happen to the maximum speed of the aircraft?
A: There will be no effect on the maximum speed;
B: The maximum speed will go up about 1.25 times;
C: The maximum speed will go up about 1.4 times;
D: The maximum speed will double.
7. The diagram shows an air bearing, which uses air as a lubricant.
Which one of these would NOT be an advantage of an air bearing?
A: It prevents metal to metal contact;
B: Very high shaft speeds are possible;
C: Components have to be made with very high precision;
D: The friction is much lower than with an oil bearing.
8. Oil lubrication systems reduce friction between metal parts in an engine. Which one other statement is true about oil lubrication?
A: It helps to cool the bearings;
B: It eliminates friction altogether;
C: The oil will last as long as the engine;
D: The most effective lubricants have boiling points less than 40 oC.
9. Which one of these statements is NOT true about the coefficient of friction?
A: Itís the ratio between the pulling force and the normal force;
B: It has no units;
C: Its value when surfaces are stationary relative to each other can be different to the value when surfaces are moving relative to each other.
D: Its value can never be greater than 1.0.
10. Which one of these statements is true about the maximum angle at which an object will stay static on a slope?
A: It depends on the weight of the object alone;
B: It depends on both the weight of the object and the coefficient of friction between the object and the surface of the slope;
C: It depends only on the coefficient of friction between the object and the surface of the slope.
D: It depends on none of these factors.