Theory of Machine
The tractive force is maximum or minimum when the angle of inclination of crank with the line of stroke (θ) is equal to

0° and 90°
270° and 360°
90° and 180°
135° and 315°

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Theory of Machine
Kinematic pairs are those which have

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

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