A tractor has the following specifications:
i) Engine speed = 2000 rev/min
ii) Rear wheel diameter = 115 cm
iii) Travel speed = 3 km per hour
What will be the ratio between crankshaft speed and rear axle speed?
a) 220.98: 1
b) 129.75: 1
c) 144.50: 1
d) 98.75: 1

Answer: c
Explanation: Travel speed 3 km/h = 50 m/min
Rear wheel diameter = 115 cm = 1.15 m
Linear speed of tractor = πDn
πDn = 50
n = \(\frac{50}{πD}=\frac{50}{π*1.15}\) = 13.84
Required speed ratio = \(\frac{Crankshaft \, speed}{Rear \, wheel \, speed}=\frac{2000}{13.84}\) = 144.50:1