18. Two spiral gears have a normal module of 10mm and the angle between the skew shaft axes is 50°. The driver has 20 teeth and the helix angle of it is 30°. If the velocity ratio is 1/3 and the driver as well as the follower are both left handed, find the centre distance between the shafts.
19. An object travels along a path, the equatiorr of distance 'x' travelled in time 't' is given by x = t²(2t+4), acceleration of the object at zero time in appropriate unit is-