RACK AND PINION EXAMINATION ANSWER
V. Ryan © 2003
4. When the motor is turned on it rotates at 240
rev/min (rpm) 

If gear Z rotates once then gear Y moves 3 times 

As gear Y has more teeth than gear Z then rpm is reduced 

Gear Y = 80 rpm 
Gears X and Y are combined to form a compound gear. Therefore, gear X rotates at the same speed as Y 
Gear X = 80 rpm 
(ii) How far does the platform travel in one minute? 
Gear X has 13 teeth. This number is multiplied by the
80 rpm giving the distanced moved in terms of number of teeth. 13 x 80 = 1040 teeth 
The rack moves the same number of teeth as it meshes with gear X. 
To convert this distance into millimetres 1040 (teeth) x 4mm (the pitch or distance between the teeth) = 4160mm 