## Theory of Machine The rotating shafts tend to vibrate violently at whirling speeds because

Bearing centre line coincides with the axis
The shafts are rotating at very high speeds
Resonance is caused due to the heavy mass of the rotor
The system is unbalanced

## Theory of Machine The example of completely constrained motion is a

Motion of a piston in the cylinder of a steam engine
All of these
Motion of a square bar in a square hole
Motion of a shaft with collars at each end in a circular hole

## Theory of Machine Kinematic pairs are those which have

Two elements that permit relative motion
Surface contact between the two elements when in motion
Elements of pairs not held together mechanically
Point or line contact between the two elements when in motion

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

## Theory of Machine The unbalanced force due to revolving masses

Varies in direction but constant in magnitude
Varies in magnitude but constant in direction
Varies in magnitude and direction both
Constant in magnitude and direction both