(a)(i) A machine is a device in which an effort applied at one end is used to overcome a load at another point. Machine makes work easier.
(ii) Uses of gears are: - to change speed to change direction of motion
- to magnify force.
(iii) Velocity ratio of a gear wheel is the ratio of number of teeth on driven wheel to number of teeth on driving wheel OR
Velocity ratio = $\frac{\text{Time rate of revolution/speed/radius of driven wheel}}{\text{Time rate of revolution/speed/radius of driving wheel}}$
(iv) To increase the mechanical advantage, the driving gear is made smaller with fewer teeth than the driven gear.
(b) Number of teeth on driven gear = 12.
Number of teeth on driving gear = 18.
(i) V.R. = $\frac{\text{no. of teeth on driven gear}}{\text{no. of teeth on driving gear}}$
= $\frac{12}{8}=\frac{2}{3}$
(ii) Efficiency - $\frac{M.A}{V.R}$ x 100% = x 100%
= $\frac{L/E}{V.R}$ x 100%
90 = $\frac{70/E}{2/3}$ x 100%
(iii) This is due to: - Friction between the tyres and load.
- Friction between chain and gear.