IEC College of Engineering & Technology Greater Noida Department of Mechanical Engineering

Transcription

1 IEC College of Engineering & Technology Greater Noida Department of Mechanical Engineering Engineering Mechanics Question Bank Prepared By: Prof (Dr) SS Chauhan

2 Short Question Tutorial No 1 Parallelogram Law 1) Two forces are to be added to determine the resultant force F r. Compute the angle 2) Two forces are to be added to determine the resultant force F r. Compute the angle 3) The unstretched length of the elastic cord AB is 3 m. Determine the force in the stretched cord if the cord stiffness is k = 400 N/m.

3 4. The force of 100 N acts at point A. Draw the free-body diagram of point A and calculate the force developed in cable AC. 5. Calculate the stretch in the elastic cable BA if the system is held in the equilibrium position shown. Both AB and AC are elastic cables.

4 Tutorial No 2 Moment of a Force 1. Select the answer that represents the moment of the force about point Select the answer that represents the moment of the 100N force about point O. 3. Select the answer that represents the moment of the 100N force about point O. 4. Compute the moment of the 100-N force about point O.

5 Transmissibility of a Force about a Specified System 1. Select the answer that represents the moment of the force about point O. 2. Calculate the resultant moment about point O. 3. Calculate the resultant moment about point O.

6 4. Calculate the resultant moment about point O. 5. Calculate the resultant moment about point O. 10 Calculate the resultant moment about point O.

7 11 Replace the three forces acting on the bent pipe by a single equivalent force R. specify the distance x from point O to the point on the x-axis through which the line of action of R passes. 12 Find the resultant R of the three tension forces acting on the eye bolt. Find the magnitude of R and the angle θ which R makes with the positive x-axis. 13. Replace the couple and force shown by an equivalent single force applied to the lever. Find the distance from the shaft to the point of application of the equivalent force.

8 14. Draw the free-body diagram of member AB then find out the support reaction at point A and B 15. On a sheet of paper draw the free-body diagram of member AB then find out the support reactions 16. On a sheet of paper draw the free-body diagram of member AB then list the number of unknowns.

9 Tutorial No 3 Moment of a Couple 1. Determine the couple moment by computing the moment of the couple's two forces about point A. 2. Determine the couple moment by computing the moment of the couple's two forces about point A. 3. Compute the magnitude F for each of the two forces acting on the outer circle, so that they create the same couple moment as that created by the 100-N forces acting on the inner circle.

10 4. Calculate the magnitude of the resultant couple moment of the two couples acting on the bar. M c =? 5. calculate the resultant force F r of the distributed loading and specify its location d measured from point O. F r =? 6. For the next 2 questions, calculate the resultant force F r of the distributed loading and specify its location d measured from point O.

11 Tutorial 4 1. The cable stays AB and AD help support pole AC. Knowing that the tension is 500 N in AB and 160 N in AD, determine graphically the magnitude and direction of the resultant of the forces exerted by the stays at A using a) the parallelogram law, b) the triangle rule. Answer: R = 575N at a standard angle of 247 o 2. Two forces P and Q are applied as shown at point A of a hook support. Knowing that P = 15KN and Q = 25KN, determine graphically the magnitude and direction of their resultant using a) the parallelogram law, b) the triangle rule. Answer: R = 37 KN at a standard angle of -76 o 3. Two control rods are attached at A to lever AB. Using trigonometry and knowing that the force in the right-hand rod is F 2 = 80 N, determine a) the required force F 1 in the left-hand rod if the resultant R of the forces exerted by the rods on the lever is to be vertical, b) the corresponding magnitude of R. Answer: F 1 = 89.2N R = 55.8 N

12 4. While emptying a wheelbarrow, a gardener exerts on each handle AB a force P directed along line CD. Knowing that P must have a 135-N horizontal component, determine a) the magnitude of the force P, C b) its vertical component. A 40 o Answer: P=176.2N Py =113.3N D B 5. Knowing that = 65 o, determine the resultant of the three forces shown. Answer: R = 1019N at a standard angle of 26.1 o

13 6. Knowing that = 25 o, determine the tension a) in cable AC, b) in rope BC. Answer: T AC =5.23 kn T BC =0.503 kn 7. Two forces P and Q are applied as shown to an aircraft connection. Knowing that the connection is in equilibrium and that the magnitudes of the forces exerted on rods A and B are F A = 600 N and F B = 320 N, determine the magnitudes of P and Q. Answer: Q=42.1 N P = 457 N 8. Two cables tied together at C are loaded as shown. Determine the range of values of W for which the tension will not exceed 1050 N in either cable. Answer: 0 <= W <= 609N

14 9. The cabin of an aerial tramway is suspended from a set of wheels that can roll freely on the support cable ACB and is being pulled at a constant speed by cable DE. Knowing that = 42 o and = 32 o, that the tension in cable DE is 20 kn, and assuming the tension in cable DF to be negligible, determine a) the combined weight of the cabin, its support system, and its passengers, b) the tension in the support cable ACB. Answer: T ACB =141.7 kn W=33.1 kn 10. A load of weight 400 N is suspended from a spring and two cords which are attached to blocks of weights 3W and W as shown. Knowing that the constant of the spring is 800 N/m, determine a) the value of W, b) the unstretched length of the spring. Answer: W=62.8N Lo = 758 mm

15 11. It is known that a vertical force of 800 N is required to remove the nail at C from the board. As the nail first starts moving, determine a) the moment about B of the force exerted on the nail, b) the magnitude of the force P which creates the same moment about B if = 10 o, c) the smallest force P which creates the same moment about B. Answer: a) M B = 80 Nm ccw b) P = 205 N c) P min = N at std angle 20 o 12. It is known that a force with a moment of 1152 Nm about D is required to straighten the fence post CD. If the capacity of the winch puller AB is 2880 N, determine the minimum value of distance d to create the specified moment about point D knowing hat a = 0.24 m and b = 1.05 m. Answer: d = 486 mm

16 Tutorial No. 5 Non-concurrent force systems 1. Replace the force system acting on the beam by an equivalent force and couple moment at the point (B). 2. Replace the three forces acting on the shaft by a single resultant force. Specify where the force acts, measured from end B. 3. Replace the loading on the frame by a single resultant force. Specify where its line of action intersects member AB, measured from A. 4. Replace the loading acting on the beam by a single resultant force. Specify where the force acts measured from the end A.

17 5. Replace the loading on the frame by a single resultant force. Specify where its line of action intersects member CD measured from end C.

18 Tutorial No.6 Equilibrium 1. Consider the volleyball net shown. Determine the angle formed by guy wires AC and AD. Answer: = 38.9 o 2. Steel framing members AB, BC, and CD are joined at B and C and are braced using cables EF and EG. Knowing that E is at the midpoint of BC and that the tension in cable EG is 445 N, determine a) the angle between EG and member BC, b) the projection on BC of the force exerted by cable EG at point E. Answer: a) = 65.0 o b) (T EG ) BC = N 3. Slider P can move along rod OA. An elastic cord PC is attached to the slider and to the vertical member BC. Determine the distance from O to P for which cord PC and rod OA are perpendicular. Dimensions are in mm. Answer: d OP = 240mm

19 4. The steel plate shown will support six 50-mm-diameter idler rollers mounted on the plate as shown. Two flat belts pass around the rollers, and rollers A and D will be adjusted so that the tension in each belt is 45 N. Determine a) the resultant couple acting on the plate if a = 0.2m, b) the value of a so that the resultant couple acting on the plate is 54 N m clockwise. Answer: a) M = 48.0 Nm cw b) a = 243 mm 5. The tension in the cable attached to the end C of an adjustable boom ABC is 1000 N. Replace the force exerted by the cable at C with an equivalent forcecouple system a) at A, b) at B. Answer: a) F A = 1000N at -20 o M A = 1724 Nm cw b) F B = 1000N at -20 o M B = 958 Nm cw 6. The masses of two children sitting at ends A and B of a seesaw are 38 hg and 29 kg, respectively. Where should a third child sit so that the resultant of the weights of the three children will pass through C if she has a mass of a) 27 kg, b) 24kg. Answer: a) d = m b) d = m

20 7. Three stage lights are mounted on a pipe as shown. The mass of each light is m A = m B = 1.8 kg and m C = 1.6 kg. a) If d = 0.75 m, determine the distance from D to the line of action of the resultant of the weights of the three lights. b) Determine the value of d so that the resultant of the weights passes through the midpoint of the pipe Answer: a) D = m b) d = m 8. Gear C is rigidly attached to arm AB. If the forces and couple shown can be reduced to a single equivalent force at A, determine the equivalent force and the magnitude of the couple M. Answer: a) R A = 362 N at o b) M =327 Nm 9. Two children are standing on a diving board of mass 65 kg. Knowing that the masses of the children at C and D are 28 kg and 40 kg, respectively, determine a) the reaction at A, b) the reaction at B. Answer: a) A y = kn downward b) B y = 2.49 kn downward

21 10. A T-shaped bracket supports the four loads shown. Determine the smallest distance a if the bracket is not to move. Answer: a min = 40.0 mm 11. Member ABCD is supported by a pin and bracket at C and by an inextensible cord attached at A and D and passing over frictionless pulleys at B and E. Neglecting the size of the pulleys, determine the tension in the cord and the reaction at C. Answer: T = 544 N,C = 865 N at std angle o 11. Two transmission belts pass over sheaves welded to an axle supported by bearings at B and D. The sheave at A has a radius of 50 mm, and the sheave at C has a radius of 40 mm. Knowing that the system rotates with a constant rate, determine a) the tension T, b) the reactions at B and D. Assume that the bearing at D does not exert any axial thrust and neglect the weights of the sheaves and the axle.

22 Answer: a) T= 375 N b) B = (337.5N) j ( 700N)k D = (337.5N) j + ( 280N)k 12. Three uniform, homogeneous and smooth spheres A, B & C weighing 300N, 600N & 300N respectively and having diameters 800mm, 1200mm & 800mm respectively are placed in a trench as shown in Fig. above. Determine the reactions at the contact points P, Q, R and S 13. Determine the magnitude of pin reaction at B on the horizontal member BD. The smooth surface on which the structure rests is horizontal

23 14. The horizontal force 200N in Fig is applied to the slopping member BCD whose bottom rests on a smooth horizontal plane. Its upper end is pinned at B to the horizontal member AB. What couple must be applied to the member AB to hold the system in equilibrium? What is the magnitude of the pin reaction at B 15. Determine the tension in the wire AC which is horizontal. 16. Find support reactions at A, E, C& D

24 17. The frictional less pulley A shown in Fig is supported by two bars AB and AC which are hinged at B and C to a vertical wall. The flexible cable DG hinged at D goes over the pulley and supports a load of 20KN at G. The angles between various members are shown in Fig. Determine the forces in AB and AC. Neglect the size of pulley

25 Tutorial No. 7 Beam 1. One end of a split horizontal beam ACB is fixed into wall and the other end B rests on a roller support. A hinge is at point A.A crane of weight 50KN is mounted on the beam and is lifting a load of 10KN at the end L. The C.G of the crane acts along the vertical line CD and KL=4m.Neglect the weight of the beam, find the reaction / moments at A &B. 2. Determine the reactions at the beam supports for the given loading. answer: A= 270 N upward B =720 N downward 3. A 50-N force directed vertically downward is applied to the toggle vise at C. Knowing that link BD is 150 mm long and that a = 100 mm, determine the horizontal force exerted on block E. Answer: E block = 282 N