title · web viewa wing is being tested in a wind tunnel to evaluate its coefficient of drag and...

ME160 Final Exam ReviewSupplemental InstructionIowa State University

Leader: Kyle HelvieCourse: ME 160

Instructor: VariousDate: 12/6/17

Topic 1: UnitsConceptual:

1. What is the difference between lbm, lbf, and slugs? If it is said that “a 5 pound object falls” what does that mean?

2. What is the definition for newtons and pascals?

Methodological: Dimensional Consistency3. Prove, using your unit system of choice, that the ideal gas equation PV=nRT is

dimensionally consistent.

Topic 2: Trigonometry and Force DecompositionConceptual:

4. What is a force vector and how is it described?

Methodological:5. F1 = 50N, F2 = 75N, F3 = 90N, θ1 = 34°, θ2 =13°,

and θ3 = 79°. Without doing any calculations, estimate the location of the resultant force, and then calculate the resultant force. Draw both your prediction and your actual vector on the diagram.

6. For the force components Fx = 15N and Fy = -7N, what is the resultant vectors direction and magnitude?

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Topic 3: Moments and Sum of ForcesConceptual:

7. What is a moment?

Methodological:8. Find the moment generated about

base of the light pole by the force F=150N.

9. Find the moment generated about point O by the two forces F1 = 35N, θ1 = 45°, and F2 = 16N (Fig. 4)

Topic 4: Introduction to Static AnalysisConceptual:

10.What does it mean for a system to be in equilibrium?

11.What are the various possible depictions of pinned and roller connections?

Methodological:12. If M=40kg, what must be A’s mass for the

system to be in equilibrium? (Fig. 5)


Fig. 4

Fig. 5




13.Provided that all segments of the bridge are of length 2m, what are the necessary reaction forces in A and B for the bridge to be in equilibrium? (Fig. 6)

Topic 5: Materials and StressesConceptual:

14. Draw a stress-strain graph. Include labels for: elastic region, stress axis, strain axis, modulus of elasticity, yield stress, plastic region, fracture point.

15. Describe stress, strain, and modulus with their respective equations.

16. What is factor of safety?


Fig. 6




Note: Shear Stress versus Tensile Stress

Tensile Stress Shear Stress

Methodological:17. In laboratory testing, a 5mm

diameter, and 50mm long test specimen of unknown material is found to elongate.003mm when experiencing a 500N force. What is the modulus of this unknown material?

18. A pinned supports reaction forces are shown on the diagram. They are found to be Fx = 400N and Fy = 600N. If the pin is 6mm in diameter and made of 1020-HR steel, what is the shear stress in the pin? What is its factor of safety?





Topic 6: Buoyancy Conceptual:

19. Under what conditions will an object float?

Methodological:20. A standard basketball (mass = 624 grams; 24.3 cm in diameter) is held fully

under water. When released, does the ball sink to the bottom or float to the surface? If it floats, what percentage of it is sticking out of the water? If it sinks, what is the normal force, FN with which it sits on the bottom of the pool

21. A standard Olympic diving pool is 5m deep. Assuming it is filled with freshwater, what is the increase in pressure at the bottom of the pool?





Topic 7: Thermal and Energy SystemsConceptual:

22.What are the three modes of heat transfer and their defining characteristics?

23.What is the difference between a closed and open thermodynamic system?

Methodological:24.A 3kg steel ball is released from rest. After falling one meter, it collides with a

spring. What is the maximum compression of the spring, given that it has a spring constant of 3000 N/m? Ignore any collision behavior or energy losses.

25. A 2500lb car comes to a complete stop from 65mph. 60% of the breaking capacity is provided by the front brakes. Determine their temperature rise if each of the two cast-iron break pad rotors weighs 15lbs and have a specific heat of 0.14 Btu/(lbm * degF)

Topic 8: Drag and LiftConceptual:

26.What is drag and lift respectively? What equations describe them?





27.Why might changing the angle of attack of a wing impact lift and drag behavior?

Methodological:28.A wing is being tested in a wind

tunnel to evaluate its coefficient of drag and coefficient of lift. The tunnel is configured such that the density of air is 1.225 kg/m^3 and the windspeed is 250 m/s. Tension scales measure the force of drag as 1500N, and the force of lift as 35,000N. What is the coefficient of drag and the coefficient of lift? The thickest the wing gets is 0.1m.

29. A sphere of radius .5m and density .034kgm3 is thrown from a passenger jet. If the

sphere has a drag coefficient of 0.25, and the density of the air is .4135 kg/m^3, what is the maximum velocity the sphere can obtain?





Visualizations and Topic Summaries

This section contains some potentially useful visualizations and explanations for specific ME160 engineering topics.

Force Vectors:Tensile Stress Shear Stress

Moments:

:

Stress-Strain Curve:

The first case shown in the moments section shows a force acting on a particle. In any force-particle system, the force can only cause some displacement Δx. Many objects can be modeled similarly by treating their centers of gravity (or centers of mass) as particles. Thus, when a force acts on the center of gravity of an object that object only moves with some displacement Δx as well. This was illustrated in the second case.

The third case shows what happens when a force is applied some distance, “d”, away from the center of gravity. This force then causes a Δx as well as Δθ. This is effectively what a moment is: a force generating a rotation about a point on an object. Fortunately, ME160 is not concerned with the Δθ as all objects are considered to be in equilibrium thus any moment generated is countered by a reaction force.


title · web viewa wing is being tested in a wind tunnel to evaluate its coefficient of drag and...

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