Applied Mechanics - Engineering

Q1:

The vertical reaction at the support A of the structure shown in below figure, is

A 1 t

B 2 t

C 3 t

D 2.5 t.

ANS:C - 3 t

Ra(vertical) = 2t is the right answer.

Let Ra be the reaction at A perpendicular to the support. Then, Ra(Horizontal)= Racos45
Ra(vertical)= Rasin45.

Using the equation of equilibrium,
Sum of the moment about B=0.

-Rasin45°6-Racos45° 4+3*4+2*2+2*2 = 0
Ra=2√(2).
Therefore, Ra(vertical) = Rasin45=2t. We got horizontal reaction component Rbcos45°(leftward) and vertical reaction
component Rbsin45;(upward) from point B. Ok, now taking moment at A:

2t*2 + 2t*2 + 3t*4- 4*Rbsin45 -6*Rbcos45 = 0,
Or, 20 -2.828Rb -4.242Rb = 0,
Or, Rb= 2.83t.

Taking sum of load in Y direction,
Ra(up)+ Rbcos45= 2t +3t,
Ra(up) + 2.00= 5t,
Ra(up)= 3.00t -> Answer.