## Theory of Machine In a mechanism, the fixed instantaneous centers are those centers which

None of the listed here
Vary with the configuration of the mechanism
Moves as the mechanism moves, but joints are of permanent nature
Remain in the same place for all configurations of the mechanism

α = 45° - φ/2
α = 90° - φ
α = 45° + φ/2
α = 90° + φ

## Theory of Machine The secondary unbalanced force due to inertia of reciprocating parts in a reciprocating engine is given by (where m = Mass of reciprocating parts, ω = Angular speed of crank, r = Radius of crank, θ = Angle of inclination of crank with the line of stroke, and n = Ratio of the length of connecting rod to radius of crank)

m.ω².r cosθ
m.ω².r (sin 2θ/n)
m.ω².r (cos 2θ/n)
m.ω².r sinθ

l = 2p - 4
l = 2p - 5
l = 2p - 3
l = 2p - 2

sinφ
secφ
cosecφ
cosφ

## Theory of Machine The two elements of a pair are said to form a higher pair, when they

Have a surface contact when in motion
Have a line or point contact when in motion
Are kept in contact by the action of external forces, when in motion
Permit relative motion