WBUT Question Papers CS Engineering Mechanics B Tech Ist Sem 2011 12

WBUT Question Papers CS Engineering Mechanics

B Tech Ist Sem  2011 12


Time Allotted.; 3 Hours                                             Full Marks .- 70

The figures in the margin indicate full mark

Candidates are required to give their answers in their own words

as far as practicable.

GROUP – A ( Multiple Choice Type Questions )

1. Choose , the correct alternatives for any ten of the following :

10x 1 = 10

i) Coloumn friction is between                      .

■ . . %

a)             solids and liquids

b! dry surfaces

c) between bodies having relative motion

d} 1 none of these.                           .                  .

ill The velocity of a simple wheel and axle, with D and d as the diameters of effort respectively is

■ a) (D + d)                 ^              b) (D – d)

d                                            D

c) —                                       d) —

D                                            d


iii)          For stable equilibrium the potential energy will be

a)            maximum

b)            minimum

c)                      zero

d)            equal to kinetic energy.

iv)          The centroid of a semicircular area of radius r from the

c) —                                               d) r.


v)            Materials having same elastic properties in all directions

are called                                             .

a)        Isotropic       b) Orthotropic

c)       Composite    d) Elastic.

vi)          The work done against any conservative force is stored

. f

in the body in the form of

a)     energy                                      b) potential energy

c) elastic energy                            d) strain energy.

vii)        A pair of a force and a couple in the same plane upon a rigid body

a)            balance each other

b)           cannot modify each other

c)            produce a moment

d)           none of these .



Hooke’s law is valid up to

a)            yield point c) proportiona



xii)        Couple is a

a)            bound vector

c)            sliding vector

free vector none of these.


xiii)                                                                                                 Angle between the vectors (i + j) and {i-j) is

a)                                                                                                      90°       b) 45°

c)                                                                                                                                    0 d) none of these.






[ Turn over



( Short Answer Type Questions )

Answer any three of the following.                             .


2*. a) Define moment.

b)           In the given figure 1 weight of the block is 1600N and p0.2 • Find the value of F for impending motion. 2 + 3


6,     a) State & Prove Lame’s theorem,

b)           Two equal loads of 2500 N are supported by a flexible string ABCD at points B and D as shown in figure 2. Find the tensions in the portions AB. BC, CD of the string.2 + 3


GROUP -C ( Long Answer Type Questions )Answer any three of the following. 3 x 15 = 45

  1. a) A block of weight, Wj=200kgf resis on a horizontal surface and supports on top of it another block of weight U2 = 5p kgf. The block W2 is attached to a

vertical wall r<by the inclined string AB. Find the magnitude of the horizontal force P applied to the lower block as shown, that will be necessary to cause slipping to impend. The coefficient of static friction for all contiguous surfaces is \x = 0.3              ■                              7


b)            A shot is fired with a bullet yrith an initial velocity of 40m/s from a point 20m iivfront of a vertical wall 10m high. Find the angle of projection with horizontal to enable the shot to just clear the wall.                      8

 stress there is to be limited to 140 N/Mm2, Find also the length of the middle portion of the total elongation of

the bar is to be 0.16mm. Take E = 2 x 2xl05mm2. 10


1                 Figure 5

b)            Determine the co-ordinate of the centroid with respect to the given axis of the shaded area as shown in figure 6.                                                 5

a) State principle of transmissibility.

b)    Given a force F = 1 Of + 5j + A kN. If this force is to have a rectangular component of 8N along a line having unit vector r = 0,6i + 0.8 k, what should be the value of A ? What is the angle between F and r ?


c)     Two identical blocks A and B each having weight W are connected by rigid link and supported by a vertical wall and a horizontal plane having same co-efficient of friction (|i) as shown in figure. If sliding impends for 0=45° , calculate (a.                                                                       2 + 5 + 8

  1. a) If the string fAN is horizontal, find the angle that the string AC makes with the horizontal when the ball is in a position of equilibrium. Also find the pressure R between the ball and the plane.



b)           A Toller of radius r = 12 cm and Q = 500 kgf is to be rolled oyer a curb of .height h = 6 cm by a horizontal force F applied to the end of a string wound around the circumference of the roller. Find the magnitude of P required to start the roller over the curb. There is sufficient friction between the roller surface anu the edge of the curb to prevent slip at A.



.           Figure 9

‘                                                                  7 + 8

1 j a| State parallel axis and perpendicular axis theorem -oi moment of inertia.,. .

b)           Define radius of gyration. How Is it related to mass moment of inertia ?                 _

c)            Determine fthe centre of a quarter circular arc ol

3.    The position co-ordinate of .a particle which is confined to move in a straight line is given by S-2(3-24t+6. where S is in m and t is in sec.



a)           the time required for the particle to reach a velocity of 72 m/s from its initial condition at t = 0.

b)           the acceleration of the particle when v = 30 m/s.

c)            the net displacement of the particle during the inteival from t =1 sec to t = 4 sec.

4.       Define (i) Malleability (ii) Resilience ini) Toughness (iv) Ductility and (v) Proof Resilience.

5.      A force F =3/ – 4/’ + 12k acts at a point A whose co-ordinates are (1, – 2, 3). Compute.

a)           moment of force about origin,

b)           moment of force about point (2.12)

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